9.1.1 Requirements for Water Supply Design

(1) The water supply system in the clean operating department shall have two inlets, the pipelines shall all be concealed, and anti-condensation measures shall be taken.

That the water supply system shall have two inlets means that intermittent water supply is not permitted and dual-direction supply shall be adopted. The water supply of the operating department shall be guaranteed by two independent mains, so that when one fails, the other can be put into use immediately. If there is only one water supply pipe, a storage tank shall be installed or a second water source shall be added to ensure safe water supply. The storage tank shall be equipped with water level control and emergency alarm facilities. When the water source is insufficient or the float is damaged and the water level is low, an alarm must be given to draw the attention of management personnel so that the water demand during surgery can be met in time.

(2) The water supply in the clean operating department serves, first, as domestic water for the medical staff and water for hand scrubbing and cleaning surgical instruments, so both cold and hot water are required; and second, as water for washing down walls and flushing floors. Water quality directly affects indoor cleanliness and the quality of surgery. Therefore, the water supply must not only be uninterrupted, but its quality must also be reliable, and the water quantity and pressure must be guaranteed.

(3) To ensure the cleanliness of the clean operating room, equipment inside the room should be kept to a minimum; therefore, the pipelines passing through the clean operating room and the pipelines in the scrub room shall be concealed. Pipelines shall be concealed in technical mezzanines or pipe shafts. Concealed pipelines must also be properly insulated and provided with anti-frosting measures; it is advisable to wrap the outside of the pipes with felt, fiber cotton, polyethylene foam pipe shells, etc., so as to maintain the temperature and humidity of the operating department and, at the same time, to prevent the walls from becoming damp and the plaster from peeling off, which would impair wall quality and the architectural appearance. The insulation layer on the pipelines shall be wrapped tightly, uniformly, and firmly, with a smooth surface. If sterile water and cooling water systems are needed in the operating department, their pipelines should not be led into the operating room, but to the adjacent auxiliary rooms.

(4) Sealing measures are an important link in ensuring indoor cleanliness. Properly sealing the pipelines that penetrate into the clean operating room prevents dust from unpurified outdoor air from entering the room and prevents purified indoor air from leaking outward, which would affect the indoor positive pressure value, while also reducing the consumption of indoor energy. Therefore, pipelines passing through walls and floor slabs shall be provided with sleeves for sealing, and there shall be no joints in the pipe sections inside the sleeves. The space between the pipe and the sleeve shall be filled with impervious elastic material. These sealing materials must also be non-combustible and non-dust-generating, and must be sealed firmly and tightly.

(5) Pipe shafts shall have dimensions sufficient for maintenance and repair, and access doors shall be provided to facilitate routine management, so that once a water pipe leaks, repairs can be organized promptly. If the pipe shaft is very small, access openings must also be provided at the valves and at the inspection openings of the drainage pipes, so that in the event of a pipe leak, repairs can be carried out without damaging the partition wall. Access doors or access openings may be omitted only when the pipes have no possibility of leaking under normal conditions.

(6) There are numerous pipelines of various kinds in the clean operating department—water supply and drainage, medical gases, heating, ventilation, air conditioning, refrigeration, cooling, lighting, telephone, and others. Whether they are located in pipe shafts, in mezzanines, or in suspended ceilings, the various pipelines often crowd, cross, and collide with one another in plan and elevation. Without comprehensive coordination and proper construction and installation, maintenance and management will be greatly inconvenienced, affecting normal use in the future. Therefore, the integrated design and construction of pipelines is an issue that must be taken seriously in today's building services design.

(7) The connection between water supply pipes and sanitary fixtures and equipment must have an air gap; direct connection is strictly prohibited. Water supply pipes must not be connected directly to any sanitary fixture or equipment that may cause contamination, unless an air gap device is provided in such a connection system or an effective backflow prevention device is installed; otherwise, contaminated water may flow back from the sanitary fixtures and sanitary equipment into the water supply system due to back pressure, backflow, overpressure flow, and other causes, contaminating the drinking water, and the consequences would be quite dangerous. Therefore, the minimum air gap by which the water outlet of the water supply pipe should be above the overflow water level of the water-using equipment shall not be less than 2.5 times the diameter of the water supply pipe at the outlet. For installations where an air gap cannot be provided, such as delayed self-closing flush valves, vacuum breakers shall be installed. The outlet of the float valve on the flushing tanks of water closets and urinals shall be at a distance of not less than 25mm above the overflow outlet of the overflow pipe.

(8) Water supply pipes shall be stainless steel pipes, steel pipes, or plastic pipes for water supply. For a long time, galvanized steel pipes have occupied the main market for water supply piping, and the corrosion problem of galvanized steel pipes has drawn more and more attention. Because rusty water causes many difficulties for drinking and management, some developed countries and regions have long since banned its use. In China, provinces and municipalities have already begun to implement the replacement of galvanized steel pipes. Document No. 0141 [1998] issued by the Shanghai Municipal Construction Commission of China stipulates: from May 1, 1998, the design of galvanized steel pipes is prohibited and the use of plastic water supply pipes is to be promoted. In 1999, four ministries and commissions under the State Council issued the "Notice on Eliminating Outdated Products in Residential Construction" (Document No. 295), stipulating that from June 1, 2000, cold-galvanized steel pipes shall be prohibited for indoor water supply pipelines in newly built urban residences, and hot-galvanized steel pipes shall be gradually banned within a time limit according to local conditions; new pipe materials such as aluminum-plastic composite pipes, cross-linked polyethylene (PE-X) pipes, and type-3 random copolymer polypropylene (PP-R) pipes are to be promoted and applied, and copper pipes may be promoted and applied in places where conditions permit.

As a result, many new water supply pipe products have appeared in China's construction market, with domestic and imported products emerging one after another. They can be roughly divided into three types: plastic pipes, metal pipes, and composite pipes.

[Reference] Plastic pipes have the advantages of good chemical stability, good hygienic conditions, low heat conduction, smooth interior with low resistance, easy installation, low price, and materials that are basically non-toxic and cause no secondary pollution; their disadvantages are poor impact resistance, poor heat resistance, and a large coefficient of thermal expansion.

Among metal pipes, the most favored are copper pipes. It is understood that copper pipes are widely used in building water supply and hot water supply in economically developed countries and regions. In the United States and Canada, more than 80% of water supply pipes are copper pipes, and in Hong Kong copper pipes are used in 50% of water supply systems. Copper pipes have the longest history of use, good mechanical properties, high pressure-bearing strength, stable chemical properties, and corrosion resistance; their service life is 3~4 times that of galvanized steel pipes, with a complete range of pipes and fittings and a variety of jointing methods. In addition, copper has antimicrobial properties that can inhibit the breeding of bacteria, especially E. coli; more than 99% of bacteria in water will disappear on their own within 5h of entering copper pipes. Therefore, copper pipes are the pipe material of first choice.

Stainless steel pipes have high strength, good rigidity, smooth inner walls, an attractive appearance, and no secondary pollution, and are therefore also highly regarded; they are developing toward reduced wall thickness and lower cost.

The third type, metal and non-metal composite pipes, combines the advantages of metal pipes (high strength, good rigidity) with those of non-metal pipes (corrosion resistance, smooth inner walls, no scaling). The disadvantage of composite pipes is that the thermal expansion coefficients of the two materials differ considerably, so they are prone to separating. The plastic-lined pipes of a certain pipeline Co., Ltd. in a certain city use a special process to machine a raised mesh pattern on the inner wall of the steel pipe, greatly increasing the friction between the outer metal pipe and the inner plastic pipe, thereby effectively reducing the inconsistency in thermal expansion between the inner and outer pipes; their service life is 5 times that of galvanized steel pipes. For water supply pipes used in clean operating departments, pipe materials with good safety performance and hygienic performance must be given full consideration.

9.1.2 Water Supply Pipelines and Design Principles

In design, one should proceed from the overall picture so that the pipelines are properly arranged, adopting the following principles of comprehensive design and mutual avoidance:

(1) Pressure pipelines yield to gravity-flow pipelines, because gravity-flow pipelines have slope requirements and cannot be raised or lowered at will.

(2) Water supply pipes yield to drainage pipes, because drainage pipes are mostly gravity-flow pipes and the waste inside them is prone to blockage; therefore, they should run as straight as possible and discharge directly outdoors.

(3) Pipelines with few fittings yield to pipelines with many fittings, which facilitates construction operations, maintenance and repair, and replacement of fittings.

(4) Pipelines requiring frequent maintenance should be placed on the outside.

When various pipelines are arranged at the same location, they should, as far as possible, run in straight lines, be parallel to one another, and not cross; consideration should also be given to reserving operating clearance for construction installation, maintenance and replacement, and space for setting up supports and hangers, so as to leave room for thermal expansion compensation, etc.

(5) The strength test and air-tightness test of water supply pipelines must comply with the design requirements and construction specifications.