Chlorination / clean and chlorination / clean and disinfection generally refers to the act of charging the water system with a suitable chemical (typically sodium hypochlorite (chlorine) or silver stabilized hydrogen peroxide) for a certain length of time to achieve chemical disinfection of the relevant pipework/plant.
The process is most common within water tanks. The procedure is as follows:
(Assuming the building is empty and the chemical chosen is sodium hypochlorite (chlorine))
1) The cold water storage tank is drained down, often with the aid of a submersible pump for larger storage tanks.
2) The water tank is then cleaned, using appropriate scrubbing brushes, descaled as necessary, and all debris removed using a wet vac.
3) The tank is then refilled with fresh water, with chlorine added to achieve 50ppm free chlorine.
4) The main to the tank is then shut off whilst engineers walk around the building opening all taps and other outlets, testing the water until 50ppm of free chlorine shows at the taps.
5) The engineers return to the tank, refill and re-dose to 50ppm. The tank is then left for 1 hour contact time, and re tested. Should the free chlorine have fallen below 35ppm, the tank is neutralized, drained and steps 3 and 4 are repeated. If the free chlorine level is above 35ppm the tank can be neutralized and refilled with fresh water, ready to flush out the remainder of the system.
This rough guide does not include variations and information on correcting ph levels. Should you contract a company to clean your cold water tanks, you should ask for independant certification to ensure the operatives have recieved a suitable level of training prior to commencement of the works.