Super chlorination is a technique used to clean and disinfect water holding vessels that cannot be washed in the traditional sense. This is different from your standard disinfection, which is for cleaning the water, not the container. Super chlorination is used when reservoirs become contininated with microorganisms or have been emptied for any reason (indicating possible esposure to contamination).
Super chlorinating is simple. On a very basic level, it is just adding a large amount of chlorine to a reservoir either as a wash applied directly to the wall or as a very strong chlorine/water solution which fills the entire reservoir.
On a more specific level, it is dependant on the strength of the hypochlorite and the amount of time the chlorine is left in direct contact with the container. The stronger the chlorine the less time required. For example, if you decide to spray the walls with straight 10% sodium hypochlorite then there is almost no time required. Whereas the normal chlorine levels in most municipal drinking water systems is not enough to ever disinfect the vessel it is in. Those low levels of chlorine will only protect the water from contamination in a reservoir that is already free of contamination.
Now you might be asking how to figure out how much chlorine to add to make super chlorinated water. If you think all you need is to dump a large amount of chlorine in then I will point out that releasing large amounts of super chlorinated water into the environment is illegal in most jurisdictions. So it is necessary to calculate how much dechlorinating agent is needed. The easiest way to know the dechlorinating needs is to measure the amount of chlorine added. In order to save money or time it is best to calculate the ammount of chlorine necessary.
50 mg/L (50 ppm) of available chlorine is a great place to start. 50 mg/L left for 24 hours will meet the best pratices and standarized procedures for most jurisdictions in North America. Below is a table outlining how much chlorine you need to add for various volumes of water.
From this chart you can see exactly how much chlorine to add. Add the hypochlorite solution when the system is haIf full. Then fill the tank or reservoir the rest of the way with clean water. If you are disinfecting something with plumbing, like a building or a boat, then make sure the super chlorinated water makes it to each cold water faucet by flushing until you can smell chlorine (or can measure it). Do not flush the hot water faucet. all you will do is waste chlorine and hot water.
This procedure will disinfect any reservoir. Regardless of the levels of bacterial contamination, because if it doesn’t work the first time repeat the process until it does. The most likely culprit if super chlorination doesn’t work the first time is that a pipe connected to the tank wasn’t flushed completely.
Whether you have a large tank of reserve water or your rain barrels start growing dangerous microorganisms, you may need to super chlorinate one day.