Our standard treatment is chlorine, the disinfectant set out in WHO guidance for water storage tanks. This page explains what we use, why, and what it means for your water.
Chlorine is used on every job. The other products are used when the tank or the client calls for them.
| Chemical | What it is | When we use it |
|---|---|---|
| Calcium hypochlorite | A solid chlorine compound, supplied as granules or powder | Standard disinfectant |
| Sodium hypochlorite | Liquid chlorine, the active ingredient in bleach | Standard disinfectant |
| Silver hydrogen peroxide | A chlorine-free disinfectant | When a client specifies it |
| Descaler | A product that loosens scale and mineral deposits | When a tank has heavy scale |
| Anti-algae coating | A protective coating for the inside of the tank | On request |
| Client-approved products | Any disinfectant on a company's own approved list | For commercial and industrial clients who require it |
Calcium hypochlorite and sodium hypochlorite both release chlorine when they are mixed with water. That chlorine is what kills the bacteria, viruses and algae living on the walls and floor of a tank. It is the same disinfectant that water utilities around the world add to drinking water.
The WHO technical note on cleaning and disinfecting water storage tanks describes chlorination as the most common way of disinfecting a water tank, and names high-strength calcium hypochlorite as the usual source of the chlorine. The CDC guidance on cleaning cisterns uses unscented liquid bleach, which is sodium hypochlorite. These are the two compounds we work with.
Chlorine has one limit worth knowing. It disinfects the tank on the day of the cleaning. It cannot protect the tank from what arrives afterwards. If line, tanker or boring water brings in fresh silt a few days later, that is the incoming water, not a failure of the disinfectant.
Disinfection is one stage of the job, and it only works if the stages before it are done properly.
A disinfectant works on a clean surface. Sludge and slime shield the bacteria underneath, so the tank is drained, the sludge taken out, the walls and floor pressure-washed, and the waste water vacuumed away before any chemical is used. See the full procedure
The disinfectant is measured for the size of the tank and mixed with clean water. We work at a controlled strength of 50 to 200 parts per million of chlorine.
The solution is applied to the walls, the floor, the corners and the underside of the cover, so that no part of the tank is missed.
Chlorine does not work instantly. The solution stays on the surfaces long enough to do its job. Strength and time go together: a stronger solution needs less time, a weaker one needs more.
The surfaces are rinsed with clean water and the rinse water is drained away. Only then is the tank refilled.
For a tank that can be taken out of use, the WHO method is to add 80 grams of high-strength calcium hypochlorite for every 1,000 litres of capacity, fill the tank, and leave it closed for 24 hours. Doubling the chlorine shortens that to 8 hours. The tank is then emptied, refilled, left for about 30 minutes, and emptied once more.
A household tank usually has to be back in use the same day. So on our jobs the disinfectant is applied directly to the cleaned surfaces at working strength and then rinsed off, instead of filling the whole tank and waiting a day.
Used correctly, yes. Chlorine is already in the water that utilities supply, at a low level. The solution used to disinfect a tank is far stronger than that, which is exactly why the last stage of the job is rinsing: the disinfectant is washed off the surfaces and drained out before the tank refills.
A faint chlorine smell in the first water after refilling is normal, and it fades as the water is used. A strong smell that does not go away is not normal. If that happens, call us on 0313-2796778.
Chlorine at these strengths is used on cement (RCC), plastic and fiber tanks. We do not use harsh acids, which are what damage a tank.
Some products have no place in a tank that holds drinking water.
The chemical is not always our choice.
Some companies let us choose the disinfectant. Others require one from their own approved list. In that case the job is done with the product they specify.
Commercial and industrial clients receive a cleaning certificate that states the chemical used, for their auditors or the health department.
Chemicals are kept in labelled containers, mixed to the stated ratio, and handled with gloves and eye protection. Safety data sheets are available on site.
Water that contains disinfectant is directed to a proper drain, not left to run onto open ground. How we work safely
Our standard disinfectant is chlorine, in the form of calcium hypochlorite or sodium hypochlorite. Chlorination is the method set out in the WHO technical note on cleaning and disinfecting water storage tanks. Where a commercial or industrial client requires a different approved product, such as silver hydrogen peroxide, we use that instead.
Yes, when it is used correctly. Chlorine is the same disinfectant that water utilities add to drinking water. The solution used to disinfect a tank is much stronger than what is in tap water, which is why the tank is rinsed and the rinse water drained before the tank refills.
You may notice a faint chlorine smell in the first water after the tank refills. That is normal and fades as the water is used. A strong smell that does not go away is not normal, and you should call us.
Once the tank has refilled. The disinfectant is rinsed out and the rinse water drained before the tank is filled again, so there is nothing further to wait for.
Household bleach is a weak solution of sodium hypochlorite, which is one of the two chlorine compounds we use. The difference is in the method: the right amount for the size of the tank, applied to surfaces that have already been cleaned, and rinsed off afterwards. Scented bleach, or bleach with added cleaners, should never go into a water tank.
No. We do not use harsh industrial acids, which can damage the tank. Sludge and deposits are removed by pump, pressure washer and vacuum, and the disinfecting is done with chlorine.
Yes. Some factories and commercial clients have their own list of approved disinfectants, and we do the job with the product they specify. Tell us when you book the survey.
Yes. Disinfection is part of every job and is covered by the rate you are quoted. See our water tank cleaning charges.
See your rate online in under a minute, or call us with any question about the chemicals.