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This question is coming up a lot at the moment as many tanks are smelling awful and/or have high bacteria levels. The simple answer here is NO – there are better, healthier alternatives than adding chemicals like chlorine or bleach to your drinking water.


Adding chlorinated water or raw bleach to a dirty water tank is asking for trouble. If your water tank has been cleaned and scrubbed using chlorine for disinfection and you drain the tank afterwards, that is OK; go ahead and use it. But seriously, who will fill up a tank with three loads of tanker water, sterilise it and then empty it to refill it with three more loads? And where are you going to dump 25,000 litres of highly chlorinated water?

The key here is – EVERY rainwater tank is dirty! You have zero ideas about what is in your water tank because you can’t see most bacteria/giardia/e.coli with the naked eye. Therefore, you also cannot tell how much organic material is in your rainwater tank.


So what are the consequences of adding chlorine or bleach to my rainwater tank?

The most significant risk is the production of…/drinking-water-cancer-risk in your water tank by adding chlorine/bleach. These chemicals react with the organic material in your dirty water tank and develop byproducts such as trihalomethane or Haloacetic acids. It is not new and well documented that they are carcinogenic.

The correct dosage of raw water in your tank is difficult to calculate. What impurities are in your tank? What bacterial loads are in your tank? Are there parasites in your tank that don’t react to chlorine, like Giardia? Is your water potable and safe to drink after using chlorine? How would you know? Do you use 1 litre or 2 litres or 3 litres per 25,000 litres? At the end of the day, you are guessing at the level of contamination in the tank and bringing a significant health risk to your water tank.


So why take the risk of a chlorine water treatment?

There are much better ways to shock dose your tank, like “Pour & Go” or installing a decent filtration system. Hydrogen Peroxide is a much safer alternative to chlorine/bleach, but it is not designed as a permanent solution to sterilising your water tank. The best long term solution is to clean your tank regularly, install a pre-tank filter and then use a Point of Entry filtration system such as a UV filter to treat the water going into the house properly.

Everyone deserves to drink safe potable water without fear of bacteria, E.Coli or parasites such as Giardia. A bit of long term thinking and planning can set you up for a lifetime of safe drinking water. The old Kiwi adage of “she’ll be right mate” may be ok on the race track, but not when your health is at risk from drinking dodgy water!

We offer a free onsite appraisal at your place where we can do a ‘WOF’ on your rain harvesting set up and make recommendations and solutions based on best industry practice. Give us a call at 0212 787 427 if you want more information regarding this topic or a permanent solution.