The laboratory water supply and drainage system is a specially designed system based on the building's water supply and drainage, featuring non-standard design and a variety of flexible layouts.

The design of the laboratory water supply and drainage system is completed before the architectural engineering design. It is an integrated product together with the building works and the building water supply and drainage; therefore, the design must be determined by professionals according to the water supply and drainage requirements of the laboratory benches configured in the laboratory, after which the overall water supply and drainage layout of the project is designed.

I. Water Supply System

As an important base for scientific research, laboratory safety and hygiene are of vital importance. This is especially true for special laboratories, such as medical infectious virus research laboratories and biological laboratories, whose safety is even more important, and the role of the water supply and drainage—an indispensable part of experimentation—must not be underestimated. The laboratory water supply system includes the laboratory process water system, the domestic water system, and the fire protection water system. Laboratory process water is divided into general laboratory water and purified laboratory water; the laboratory purified water system is an independent water supply system. The domestic water system and the fire protection water system are consistent with the water supply systems of ordinary buildings and can usually be combined with the general laboratory water system into one system.

Different laboratories have different requirements for laboratory water; the quality of recirculating cooling water for laboratory instruments shall meet the different water quality requirements of each type of instrument. Laboratories conducting experiments with strong acids, strong alkalis, or highly toxic liquids with a possibility of splashing or explosion shall be provided with emergency shower facilities nearby; when the head of water discharged from an emergency eyewash exceeds 1 m, pressure-reducing measures shall be taken; faucets in Class II laboratories shall use foot-operated, elbow-operated, or sensor-operated switches. Indoor fire hydrants shall be located in the clean zone; the pipe entry of the water supply system should usually be located in the clean zone, using a top-down (upfeed) water supply network.

The indoor fire protection water system includes the ordinary fire protection system, the automatic sprinkler water supply system, and the water curtain water supply system. Buildings such as laboratory buildings and warehouses shall have an outdoor fire protection water supply system when necessary, consisting of outdoor fire water pipes, outdoor hydrants, fire pumps, etc. See Figures 6-44 and 6-45.

II. Water Supply Methods

An ordinary laboratory usually needs only one service pipe; however, if the equipment of a large laboratory building requires a secure water supply, two service pipes should be provided. A single service pipe usually enters the laboratory building from the middle of the building, so that the water pressure is more balanced. With two service pipes, they usually enter from different sides of the laboratory building. If, in special circumstances, they can only enter from the same side, a large spacing—no less than 10 m—must be maintained between the service pipes, and valves shall be installed on the water supply network connecting the two service pipes, so that safe water supply can still be maintained in the event of a local fault. The service pipes should be introduced from the location with the larger water consumption. In addition, the internal water supply piping of the laboratory should be rationally arranged to facilitate pipe maintenance. Internal pipe runs should be as short as possible and crossings avoided, making the water supply safer and more reliable. Piping in ordinary laboratories usually runs exposed along corridors,

[Figure: Fig. 6-44 "Laboratory Water Supply Drawing" — laboratory water supply plan/point layout (approx. 1:100), including building plan outline, room partitions, water use points, water supply pipe routing, dimension lines, and axis numbers.]

Fig. 6-44 Laboratory Water Supply Drawing

[Figure: Fig. 6-45 "Laboratory Water Supply System Diagram" — including "Water Supply System Diagram 1:100" (axonometric) and "Water Production System Diagram 1:100", showing water supply/production risers, mains, branches, valves, connections at water use points, pipe routing, and elevation relationships.]

Fig. 6-45 Laboratory Water Supply System Diagram

walls, ceilings, or column corners as exposed runs, which is convenient for observation but easily accumulates dust. Therefore, in laboratories with relatively high safety requirements, concealed installation is usually preferred, with pipes laid in pipe shafts, ceilings, pipe trenches, or common pipe galleries. It is worth noting that all concealed pipes should have access openings at the positions of control valves to facilitate fault repair. Domestic water supply pipes are often located in clean zones. For the pipe entry of the water supply system of a radioactive laboratory, the water supply network often adopts the top-down (upfeed) arrangement. Where pipes run from the clean zone to equipment in the contaminated zone—such as glove boxes, fume hoods, and showers—contamination is possible; therefore, they should

be fed via a local break tank. The capacity and height of the break tank should be appropriate, and a booster device should be added if necessary. Alternatively, at the junction between zones of different radiation levels, an isolation valve can be installed at each end of the pipe with a branch connected between them; when the pipe is not in operation, the isolation valves are closed and the drain valve opened to empty the residual water. For small radiochemical laboratories, a check valve can be installed on the pipe before it enters the contaminated zone to prevent contamination. The laboratory water supply system shall guarantee the necessary pressure, water quality, and water quantity. For large high-rise laboratory buildings, when the outdoor network cannot meet the water requirements of the upper-floor laboratories, or when the outdoor network pressure is periodically insufficient—especially to guarantee safe water supply for laboratories—local booster equipment or roof tanks and pumps shall be provided for the exclusive use of upper-floor laboratories; emergency drench showers and emergency eyewashes shall be provided, with sufficiently large water flow and quick-opening valves. Common water supply methods are as follows:

  1. Direct water supply. Where the laboratory has few floors and the water pressure and quantity are adequate, the direct supply method can generally be used; with this method no indoor booster pump is needed and the system is usually connected to the outdoor water supply network.

  2. Water supply with an elevated tank. This method can be used when, during peak water consumption, the pressure in the outdoor network drops so that the water requirements of the upper floors cannot be met, or when the outdoor network pressure is periodically insufficient.

  3. Water supply with booster pumps. This method can be used when the pressure of the outdoor network is lower than the pressure required for laboratory, domestic, and fire protection water.

Water supply and drainage facility requirements for different laboratory levels:

  1. BSL-1: Each laboratory shall have a handwashing sink near the exit.

  2. BSL-2: Each laboratory shall have a handwashing sink near the exit; eyewash facilities and emergency shower devices, etc., shall be provided.

  3. BSL-3: Handwashing facilities shall be provided at the exits of the semi-contaminated zone and the contaminated zone; the water supply shall be fitted with backflow prevention devices and use non-manual (hands-free) supply valves. Shower facilities shall be provided in the clean zone; emergency disinfection shower devices shall be provided in the semi-contaminated zone when necessary. No floor drains shall be provided inside the main laboratory; the drainage of the semi-contaminated and contaminated zones shall be completely isolated from other drainage, collected through dedicated pipes into an independent device, and disinfected and sterilized.

III. Drainage System

The laboratory drainage system is configured according to the composition, properties, flow, and discharge pattern of the wastewater discharged from the laboratory. Cooling water discharged from laboratory equipment or other wastewater containing only harmless suspended or colloidal matter need not be treated and can be discharged directly to the outdoor drainage network. Wastewater containing multiple components or toxic and hazardous substances, which may interact with each other, damage pipes, or cause accidents, shall be separated from domestic sewage and discharged through dedicated pipes to a disinfection tank for unified disinfection. Relatively pure solvent waste liquid or toxic reagents should preferably be discharged after treatment; discharged wastewater to be reused shall be treated accordingly. It is handled as chemical medical waste and must not be discharged directly into the sewage station. The layout of drainage pipes likewise needs to be rational, with as few bends as possible to

prevent clogging by impurities, and the arrangement should be relatively concentrated to facilitate maintenance after failures. Drainage pipes should run along corridors, column corners, walls, ceilings, etc., but care must be taken to avoid passing through laboratories with high safety requirements, such as precision instrument rooms. Main pipes should be arranged as close as possible to equipment with larger drainage volumes. Small laboratories with small wastewater volumes may use a single drainage system. However, where the wastewater volume is small but its concentration high, it can be collected in dedicated containers and sent to a wastewater storage area or treated accordingly. Discharged radioactive wastewater requires special treatment: after isotope decay it is handled as medical wastewater; it must not pass through the clean zone and shall drain from the clean zone toward the contaminated zone to avoid spreading contamination. If the radiation level is high, dedicated drainage trenches, shafts, and pipe channels shall be provided, together with the necessary protective measures. If the radioactive wastewater is corrosive, appropriate corrosion-resistant materials must be selected for the pipes to avoid corrosion and leakage. Generally, pipe trenches can be built of brick; where protection is needed or the groundwater level is high, concrete must be used. The trench lining uses cement render, carbon steel, or stainless steel facing, painted with anti-rust paint. See Figures 6-46 and 6-47.

[Figure: Laboratory floor drainage plan (CAD colored drawing), showing the layout and drainage points of the functional rooms of the clinical laboratory department; room labels include: fresh air plant room, storage room, HIV immunology laboratory area, product analysis area, amplification area, specimen preparation area, reagent preparation area, washing room, buffer area, preparation area, dedicated corridor, inoculation and culture room, sputum testing room, body fluid room, identification room, sterile room, disinfection room, phlebotomy room, large floor-standing instrument area, biochemistry, immunology, hematology, clinical testing, waiting area, women's/men's changing rooms, water production room, UPS, cold storage, specimen storage room, pathogen molecular diagnosis room, tissue typing laboratory, cell room, trace elements, specimen processing room, VIP blood draw room, report issuing area, meeting room, archive room, laboratory department office, director's office, duty room, etc.]

Fig. 6-46 Laboratory Drainage Drawing

[Figure: Axonometric diagram of the laboratory drainage system, with pipe diameter labels such as De50/De75/De110, slope and elevation symbols, branch pipes/risers, floor drains and cleanouts; titled "Drainage System Diagram 1:100" in the figure]

Fig. 6-47 Laboratory Drainage System Diagram

1. Composition and Hazards of Wastewater

Wastewater generated by laboratories includes surplus samples, analytical sample residues, expired stock solutions and washing solutions, and large quantities of rinse water. Almost all routine analysis items have wastewater pollution problems to varying degrees. The composition of this wastewater is all-encompassing, including the most common organic matter, heavy metal ions, and harmful microorganisms, as well as relatively rarer cyanides requiring separate treatment; bacteria, toxins, etc. must be sterilized.

Once wastewater containing excessive heavy metals is discharged downstream into clean water, it contaminates large areas of water; because such heavy-metal-contaminated water is indistinguishable from normal water in color and odor, once it is used for irrigation, the soil and crops inevitably become contaminated with heavy metals. People who eat crops grown in heavy-metal-contaminated soil are easily poisoned by heavy metals.

2. Wastewater Treatment Methods

There are generally physical, chemical, and biological methods. The physical method mainly uses physical action to separate suspended matter from wastewater; the chemical method mainly uses chemical reactions to treat dissolved or colloidal substances in wastewater; the biological method removes colloidal and dissolved organic matter from wastewater. Each of the three basic treatment methods has its own characteristics and applicable conditions. Before wastewater is discharged into the municipal network, the degree of treatment shall be determined according to discharge requirements, taking into account the self-purification capacity of the receiving water body; the permissible load of the water body—i.e., the permissible concentration discharged into it—is usually determined from indicators of harmful substances and dissolved oxygen.

2.1 Treatment of Acidic Wastewater

Neutralize with alkaline wastewater so that the pH of the mixed wastewater approaches neutral; add neutralizing agents to the acidic wastewater; or filter the acidic wastewater through an alkaline filter bed for neutralization.

2.2 Treatment of Alkaline Wastewater

Neutralize with acidic wastewater; add acidic neutralizing agents to the alkaline wastewater;

sparge flue gas (acidic gases such as carbon dioxide or sulfur dioxide) into the alkaline wastewater; or use carbon dioxide dissolved in water to neutralize alkaline wastewater.

2.3 Treatment of Mixed Waste Liquids

The process "water quality homogenization + neutralization filtration — neutralization coagulation — displacement internal electrolysis — biological adsorption tank — sedimentation tank plus clear water tank" is adopted. In wastewater treatment, to protect the online pH control system, neutralization filtration technology is used to ensure that acidic and alkaline wastewater stably meets the discharge standard, and reagent consumption is saved. Combined packing is used to immobilize sludge; the disinfection step uses an advanced ozone generator; sludge digestion uses a pulse water distributor to achieve sludge reduction. This process can decompose complex organic matter and stably treat the effects of reagents in laboratory wastewater. Moreover, the process has low operating costs, convenient management, and a wide range of applicability.

Through rational layout, the footprint is minimized; with good landscaping design, the sewage station is rationally planned to become a feature within the laboratory center.

2.4 Treatment of Special Wastewater

Wastewater containing radionuclides shall be divided, according to the half-life of the nuclides, into long-lived and short-lived radionuclide wastewater, which shall be treated separately. For wastewater containing long-lived radionuclides at relatively high radioactive concentrations, the wastewater shall be stored centrally; once a certain quantity has accumulated, it is treated by purification methods, and the small amount of concentrate produced during purification can be treated by solidification. Short-lived radionuclide wastewater shall be treated by the storage method. The treatment of wastewater containing radionuclides shall comply with the current GB 8703-88 Regulations on Radiation Protection. Sewage from Biosafety Level 4 and Biosafety Level 3 laboratories must be disinfected; after treatment, the sewage shall comply with the Discharge Standard for Hospital Sewage. See Fig. 6-48.

[Figure: Sewage treatment process flow diagram. The sequence is: laboratory wastewater → water quality homogenization tank → neutralization filter tank → neutralization tank (connected to a blower, dosing acid and alkali) → sedimentation tank (sludge discharged to the sludge digestion and thickening tank) → internal electrolysis displacement tank → biological adsorption tank → disinfection tank (ozone supplied by an ozone generator) → clear water tank → compliant discharge. Note in figure: screenings and sludge are disinfected and then transported out together with hazardous waste for harmless disposal.]

Fig. 6-48 Sewage Treatment Process Flow

IV. Precautions for Water Supply and Drainage System Design

  1. The laboratory water supply and drainage system shall be scientifically designed to ensure that the water source is not contaminated; if the sources of laboratory water and drinking water differ, the drinking water and laboratory water faucets shall be labeled separately to avoid confusion.

  2. The laboratory building shall have a backup water source; when the municipal water supply is insufficient or interrupted, the backup source can ensure the normal supply of cooling water for various instruments, water for eyewashes, water for stills, and water for distillation flask condensers.

  3. The water supply and drainage system shall match the laboratory modules, be rationally arranged, and be easy to maintain; pipe runs shall be as short as possible and crossings avoided. Water supply and drainage pipes shall be routed along walls, columns, pipe shafts, bench cavities, fume hood liner panels, and similar locations; they must not be routed next to articles that decompose rapidly, burn, explode, or are damaged on contact with water, nor above valuable instruments and equipment. Pipes in ordinary laboratories may be installed exposed; in laboratories with higher safety requirements they should be concealed wherever possible, and all concealed pipes shall have access openings at control valves for maintenance.

  4. The water supply and drainage system shall be designed flexibly, with some facilities reserved to ensure the laboratory's reliability and continuous operation.

For top-down (upfeed) systems, the horizontal main water supply pipe should preferably be laid above the ground-floor corridor or on the basement ceiling; for bottom-up (downfeed) systems, the horizontal main should preferably be laid in the top-floor pipe service space or above the top-floor corridor; in non-freezing regions it may be laid on the roof. A valve shall be installed on each branch pipe leading from the supply main into a laboratory.

  1. The positions of water use points inside the laboratory must be scientifically located and pre-installed; water use points should be placed against walls wherever possible, facilitating the arrangement of drainage points and meeting future renovation needs.

  2. Where fully automatic biochemistry analyzers, hematology analyzers, and immunoassay analyzers are placed in the laboratory, dedicated anti-odor floor drains shall be provided, with a maximum distance between the floor drain and the instrument not exceeding 2 m.

V. Purified Water System

In today's laboratories, the water environment—the most basic environment of the vast majority of laboratories—occupies a very important position. Water quality often determines the authenticity and reproducibility of many experimental results; for experiments, the concentration of impurity elements and compounds in purified water is usually required to be at the ppb level or even lower. In laboratory scientific research, the starting point for purification is tap water; if the laboratory already has distilled water, deionized water, or reverse-osmosis water, then only the ultrapurification process needs attention.

A laboratory purified water system produces water of extremely high purity—water from which conductive media have been almost completely removed, while undissociated gases, colloids, and organic matter (including bacteria) are also removed to a very low level. Its conductivity is generally 0.1–0.055 μS/cm, resistivity (25°C) > 10×10⁶ Ω·cm, and salt content < 0.1 mg/L; ideal pure water (theoretical) is 0.055 μS/cm with a resistivity (25°C) of 18.3×10⁶ Ω·cm. See Fig. 6-49.

[Figure: Laboratory purified water supply plan (CAD drawing), showing the floor layout of a medical laboratory, with the waiting area, specimen processing area, multiple laboratories, corridors, and stair/elevator cores at both ends visible; purified water piping is shown in colored lines indicating routing and water use points, with dimensions marked around the perimeter]

Fig. 6-49 Laboratory Purified Water Supply Drawing

1. Water Purification Methods and Their Combined Application

In medical laboratories—such as biochemistry rooms, bacteriology rooms, cell rooms, immunology rooms, and hematology rooms—purified water is used.

Laboratory purified water can be produced by the following methods; ultrapure water must combine multiple technical means to fully meet the specifications.

1.1 Distillation

Distillation is a traditional method and a commonly used way to produce purified water from drinking water. According to the number of distillations, it is divided into single, double, and triple distillation; water purity increases with the number of distillations.

The advantages of distillation are its simplicity and the small one-time investment in equipment; the disadvantages are relatively high energy consumption and limited purity and output.

1.2 Filtration

This method generally first uses pre-filtration to remove large particles and silt from the water, then coarse and fine filter cotton cartridges, and finally reverse osmosis (RO). RO membranes are typically used to filter out contaminants down to 1 nm in diameter; a typical reverse osmosis process can remove 90% of ionic contamination, most organic contaminants, and nearly all particulate contamination from water. Reverse osmosis has a low removal capacity for non-ionic contaminants with molecular weights below 100 daltons, and the RO membrane's removal capacity increases as the contaminant molecular weight increases. Theoretically, this method can remove 100% of molecules with molecular weights greater than 300 daltons and particles including colloids and microorganisms; dissolved gases cannot be removed.

In the reverse osmosis process, feed water is pumped at a certain pressure (usually 4–15 bar, 60–220 psi) onto the

feed side of the RO membrane in a tangential flow. RO membranes are generally very thin polyamide membranes, stable over a wide pH range, but they can be damaged by oxidants such as chlorine in municipal water supplies. Microporous depth filters and activated carbon filter columns used for feed water pretreatment typically protect the RO membrane from large particles, heavy metals, and free chlorine. Generally 15%–25% of the feed water becomes permeate; the concentrate retained upstream contains most of the salts, organic matter, and nearly all particles. The volume ratio of permeate to feed water is called the recovery rate.

The performance of RO membranes in water purification systems is usually monitored by measuring the ion rejection rate, which is the difference between feed and permeate conductivity divided by the feed conductivity, expressed as a percentage. The ion rejection rate and recovery rate depend on feed water quality, feed pressure, water temperature, and the condition of the RO membrane.

Because of its excellent purification efficacy, reverse osmosis is a very effective technology for removing the vast majority of impurities. However, its permeate production rate is relatively low, so it is usually paired with a storage tank to hold the product water for use or further purification. The reverse osmosis unit protects downstream systems from fouling or contamination by colloids and organics; downstream systems are usually equipped with ion exchange or electrodeionization devices. To understand the desalination principle of reverse osmosis, one must first understand the concept of "osmosis." Osmosis is a physical phenomenon: when two bodies of water containing different salt concentrations are separated by a semipermeable membrane, water molecules from the side with less salt pass through the membrane into the water with more salt, while the salt does not permeate; in this way the salt concentrations on both sides gradually equalize.

(1) Pre-filtration. Filtration performed with materials having pore sizes above 5–8 μm is called pre-filtration; it is mainly applied at the inlet of water purification instruments to remove large particles from tap water.

(2) Ultrafiltration (UF). Continuous filtration with a molecular weight cutoff of 5,000 daltons is called ultrafiltration. It is mainly used for purification of biological macromolecules or removal of impurities. In ultrapure water instruments, it is mainly used to remove biological macromolecules such as nucleases and endotoxins from ultrapure water, meeting the strict requirements of biological experiments for ultrapure water.

(3) Microfiltration (MF). Filtration performed with materials having pore sizes between 0.1 μm and 5 or 8 μm is called microfiltration. It is used to remove particles and microorganisms from purified water; in-line microfilters in the flow path or point-of-use microfilters at the outlet are available.

1.3 Adsorption

The adsorption method uses the high porosity of activated carbon to adsorb and remove some microorganisms, free chlorine, and other impurities.

1.4 Photo-oxidation

Photo-oxidation uses 185 nm and/or 254 nm ultraviolet light to kill and oxidatively decompose microorganisms in water, thereby controlling the total organic carbon (TOC) level of ultrapure water.

1.5 Ion Exchange

With the continuous improvement of industrial production, ion exchange resins have also been upgraded; combined with several other technical means, they give rise to electrodeionization, an ion exchange method that can be regenerated online.

1.5.1 Classical Ion Exchange (SDI)

Generally, cation and anion resins are placed in separate vessels; after a period of use they are essentially saturated and can then be regenerated off-line. The purity of deionized water produced by this method is about 1 MΩ·cm.

1.5.2 Ion Exchange with Nuclear-Grade Resin

This is the most efficient ion exchange resin product to date; water treated with it can reach 18.2 MΩ·cm, Grade I ultrapure water. In ultrapure water instruments, nuclear-grade cation and anion exchange resins are mixed and packed in one vessel for single use; they are disposable and cannot be regenerated.

1.5.3 Electrodeionization (EDI)

This is an ion exchange method combining ion exchange, ion-selective membranes, and immediate regeneration under an electric field. EDI is an upgraded version of ion exchange.

The greatest advantage of this technology is that, in theory, it has no consumable materials; but its disadvantages are the large one-time investment and the EDI module's high purity requirements for heavy metal ions and the like in the feed water—otherwise it is easily poisoned, and under the electric field the active ion exchange resin cannot be regenerated, so the EDI module must be replaced. The true significance of EDI lies in enterprises such as pharmaceutical plants with strong certification requirements, where continuous production can be guaranteed. In the laboratory field, using an EDI module for water production increases purchase cost and is not the most efficient choice. With ion exchange, the longer the water's path through the ion exchange resin, the better the exchange effect.

(1) Using ion exchange, the process is as follows: raw water → raw water booster pump → multimedia filter → activated carbon filter → water softener → precision filter → cation resin filtration → anion resin filtration → mixed-bed cation/anion resin → microporous filter → point of use (or storage tank)

(2) Using two-stage reverse osmosis, the process is as follows: raw water → raw water booster pump → multimedia filter → activated carbon filter → water softener → precision filter → first-stage reverse osmosis → pH adjustment → intermediate tank → second-stage reverse osmosis → purified water tank → purified water pump → microporous filter → point of use

(3) Using EDI, the process is as follows: ultrapure water equipment raw water → raw water booster pump → multimedia filter → activated carbon filter → water softener → precision filter → first-stage reverse osmosis unit → intermediate tank → intermediate pump → EDI system → microporous filter → point of use

(4) Raw water → multimedia filter → activated carbon filter → water softener → intermediate tank → low-pressure pump → pH adjustment → high-efficiency mixer → precision filter → high-efficiency reverse osmosis → intermediate tank → EDI pump → EDI system → microporous filter → point of use

1.6 Combined Application of Purification Technologies

Suppliers of laboratory purified or ultrapure water often combine multiple means to convert tap water into the high-purity water required by laboratories.

2. Grading of Laboratory Purified Water

Laboratory purified water can be divided into three conventional grades: purified water, Grade II laboratory purified water, and Grade III laboratory purified water.

2.1 Grade III purified water generally has a physical purity of less than 50 μS/cm; single-distilled water, double-distilled water, ordinary deionized water, and reverse-osmosis water all belong to this grade and are generally produced by purifying tap water. The main uses of Grade III purified water are glassware washing, water for autoclaves, water for artificial environments, and feed water for ultrapure water instruments.

2.2 Grade II purified water is commonly expressed as 5–15 MΩ·cm, though the range 1–17 MΩ·cm can also be regarded as Grade II purified water; Grade II purified water is generally produced by subjecting Grade III purified water to further ion exchange or electrodeionization. It is mainly used for preparing general reagents, water for ordinary chemical experiments, and feed water for ultrapure water instruments.

2.3 Grade I ultrapure water refers to water with a physical purity greater than 18 MΩ·cm; a resistivity of 18.2 MΩ·cm is the indicator of Grade I ultrapure water. Grade I ultrapure water is produced by further purifying Grade III or Grade II purified water through nuclear-grade ion exchange resin, and it is mainly used for high-precision analytical experiments and life science experiments with very high water purity requirements.

3. Supply Modes for Laboratory Purified Water

There are two supply modes for laboratory purified water: the central supply mode and the decentralized supply mode.

3.1 Central Purified Water Supply Mode

The central purified water supply mode means that purified water production equipment is installed centrally, and laboratory water is delivered through supply piping to the water use points of each laboratory—whether a single laboratory or an entire laboratory building—so that laboratory purified or ultrapure water is obtained directly from the purified water faucet at each use point.

Advantages of the central purified water supply mode:

(1) Low operating costs and centralized management.

(2) Collective use, with no possibility of idle machines.

(3) Large output; water use is networked, with multiple draw-off points in the same laboratory.

Disadvantage of the central purified water supply mode: the system must guarantee long-term safe operation, otherwise there is a risk of water interruption.

3.2 Decentralized Purified Water Supply Mode

The decentralized purified water supply mode means that a water purification machine or finished water is provided at each water use location in the laboratory.

Advantages of the decentralized purified water supply: each instrument has its own right of use and a high utilization rate.

Disadvantages of the decentralized purified water supply:

(1) High operating costs, dispersed management, and relatively high consumption costs.

(2) Fixed-point installation as floor-standing or bench-top units, fixed-point water draw, small machine output and flow, and low work efficiency.

(3) If each experimental group purchases separately, the owner's total investment in such products is very high, and the vacancy rate may rise because of the differing workloads of each group, which is unfavorable for maximizing investment efficiency.

(4) Water quality varies.

With the development of laboratory equipment, networked and centralized laboratory water supply has become the trend for purified [water in large laboratory buildings]