Water is a best medium for many microorganisms, microorganism can be a highly pathogenic which causes serious diseases; many diseases are water born, these pathogens infect after consumption of contaminated water, a microbial seed microorganisms tend to settle on a surface if water is allowed to stand in a stagnant position for few hours, these settled microorganism form a film over the surface of vessel and piping, such film formed by microorganisms is also called as biofilm, biofilms are very difficult of remove, once a biofilm is formed at a particular point then that point may form a biofilm again even after cleaning very easily as seed from this point is may not completely get removed effectively.
Biofilms then can become a source of microbial contaminations; therefore purified water after collection in a distribution system is always kept in a closed loop in a continuous circulation.
A continuous circulation is also not enough at some points, therefore it is aided with high temperature range from 65 °C to 80°C, a minimum temperature of 65 °C is considered a self sanitizing, but better assurance is obtained in temperature range 70°C to 80°C .
Purified water collected should be stored in a stainless still vessel which must facilitate distribution to the point of use in a closed loop of continuous circulation, tank should be made of corrosion free material of construction, and facilitate sanitization and cleaning as well as cleaning validation.
While water is kept in continuous circulation loop, a slope must be maintained in piping from point of storage to the point of supply.
All drains must be able to get emptied out with gravity.
All joints and coupling in piping must not serve as a cold point so that the water temperature is dropped down at the point.
Flow of water through loop must be a turbulent flow, as it is observed that a laminar flow of water is not effective in preventing formation of biofilm, a turbulent water circulation flow through closed loop is effective in preventing formation of biofilm.
There should not be any one way dead supply points where there are chances of water remaining steady for long time and which may contribute towards microbial contamination of purified water.
Ball valves in water purification system should not be used as it can hold water inside the ball valve which can remain stagnant for time sufficient to facilitate microorganisms to grow. As well as side arm level measuring fittings should be avoided for similar reason.
Water storage vessels should remain dry in open space above water level therefore in a circulation loop tanks are provided with spray ball inlets which spray water while returning in to storage tank.
There must be sufficient sampling points in the loop from which water can be sampled without affecting the quality of water in process, from all points, to evaluate its microbial purity and to do validation of purified water for pharmaceutical use.
Ultra violate light lamps can be used to reduce a bio burden at various points like, source water input in to water purification system, at the point of starting and completion of demineralization , at the point of completion of reverse osmosis , and at few points in supply piping , near joints , and at the point of immediate final use point.