The WFI distillation system is composed of water treatment equipment, storage equipment, distribution pump and pipe network. The water production system has the possibility of external pollution caused by the raw water and external causes of the water production system, and the pollution of the raw water is the main external pollution source of the water production system. The US Pharmacopoeia, the European Pharmacopoeia and the Chinese Pharmacopoeia all clearly require that the raw water of pharmaceutical water must at least meet the quality standards of drinking water. If the drinking water standard cannot be met, pre-purification measures must be taken first. Since Escherichia coli is an obvious sign of water pollution, there are clear international requirements for Escherichia coli in drinking water. Other polluting bacteria are not subdivided, and are expressed as "total bacteria" in the standard. The limit of total bacteria in my country is 100/ml, which indicates that there is also microbial contamination in the raw water that meets the drinking water standard, which endangers the water production system. The contaminating bacteria are mainly Gram-negative bacteria. Others, such as unprotected vents of storage tanks or the use of poor quality gas filters, water backflow from contaminated outlets, etc., can also lead to external contamination.
In addition, there is internal pollution during the preparation and operation of the water system. Internal pollution is closely related to the design, material selection, operation, maintenance, storage, use and other factors of the water pollution system. Various water treatment equipment may become the internal pollution source of microorganisms. For example, microorganisms in raw water are adsorbed on the surface of activated carbon, deionized resin, filter membrane and other equipment to form biofilm, and microorganisms living in biofilm are affected by biofilm. Protection, general disinfectants will not work on it. Another source of contamination exists in the distribution system. Microorganisms can colonize and multiply on pipe surfaces, valves and other areas, forming biofilms that can be a persistent source of pollution. Therefore, some foreign companies have stricter standards for the design of water systems.