Giardia and Salmonella in rainwater tanks

Recently we have been called out to clean tanks with evidence of giardia and salmonella.  While  these two issues are quite different, they do highlight some very real problems which can occur when rainwater harvesting systems are not properly understood and maintained.

In both cases, it seems the source of the contamination was via birds or vermin on the catchment areas.

Salmonella is a bacteria (in this case most likely carried by rats) and can be treated with use of a food-grade anti-bacterial water sanitiser and water filtration treatment incorporating ultra-violet (UV) disinfection.

Giardia is a protozoan parasite.  In initial stages, it is encased in an egg, the shell of which is resistant to penetration by anti-bacterial substances.   Even UV light will not destroy it.  Due to the size, it can bypass many typical water filtration systems and it is recommended that 0.5 to 1 micron filtration is required to trap the eggs and live cysts.

Water testing to positively identify the source of the contamination is costly.  In the case of the salmonella, this occurred on a Council-owned property and a laboratory test was undertaken.  In the case of giardia, there was enough evidence that the problem originated with the tank water and the owners decided to clean the tank and install the filter without testing – preferring to spend the money on the solution.

In both cases, tank water was used for drinking and several people became quite ill as a result.

If you do want to drink your tank water (we don’t recommend this if a mains water supply is available) a thorough tank maintenance routine is essential, as is an appropriate level of water treatment and/or filtration.

rainwater harvesting, tank cleaning, tank maintenance, Water filtration, water treatment Hide