There’s a long-standing culture of tank ownership in rural Australia but it’s a relatively new phenomenon in urban Australia. If you weren’t brought up in a community where maintaining the water tank was normal practice you may not know what’s involved.

It’s true that rainwater systems, especially those that store the water in above-ground tanks, are pretty safe. But that doesn’t mean they are completely maintenance-free. Fortunately, maintaining water quality and avoiding the risk of unhealthy water only requires a little time and effort, especially if you work on prevention rather than cure.

Nevertheless, most State health departments recommend using the public water supply (if available) for drinking and cooking because this water is filtered, disinfected, fluoridated and monitored regularly.

The two main health considerations for tank water are contamination and the risk of providing a breeding ground for mosquitoes.

Water contamination

Tanks store water collected from your roof. That large exposed surface also collects leaves and other plant debris, dust, bird and animal droppings, and other animal debris. In urban areas, airborne contaminants from traffic and industry activities may also settle on the roof or attach to raindrops.

If not prevented, debris on the roof washes into the gutters and into your tank with every downpour. Birds and other small animals (possums, rats, mice, lizards, snakes) seeking refuge or water can get trapped in pipes or fall into the tank itself, fouling the water completely.

Sludge build-up

In the tank, debris and other contaminants slowly settle to the bottom, building up over time into an unpleasant dark sludge that harbours bacteria and other organisms. This sludgy sediment can taint the flavour and add an odour to your water, and the bacteria can use some of the oxygen in your water so it isn’t as sparkling as you expect.

Most micro-organisms are harmless but some, including E.coli, Giardia and Salmonella, can be a health risk. They can multiply in the sludge to levels that can cause stomach cramps, diarrhoea and other illnesses, especially in children and the very old.

Because the sludge sits below the level of the outlet pipe it is generally undisturbed and doesn’t enter your drinking water. But if the tank runs low, a burst of rain can stir it up and mix it with the water that does reach the outlet, blocking filters, discolouring the water, exuding an unpleasant odour and jeopardising your health.


Mosquitoes carry diseases, including Dengue fever and Ross River virus, as well as being annoying and unpleasant.

Prevention is better than cure

A few simple jobs will keep contamination and mosquitoes to a minimum. Essentially, if you reduce what reaches the tank, you reduce the problem.

Trees and branches

Keep your tank and roof free of overhanging branches. This will keep leaves and other plant debris to a minimum and help keep your gutters clean as well as making it more difficult for small animals to get on your roof.


One of the easiest ways to reduce contamination is to keep your gutters clear of debris that would otherwise wash into the tank.

Either clear your guttering regularly (every three-four months) or, better still, install gutter guard. Newcastle Gutter guard will keep leaf litter and other coarse contaminants out of your tank and it also serves several other functions. By preventing a build-up of leaves and other plant debris in the gutter it reduces the risk of fire started by embers from a fire or flooding caused by blocked gutters and downpipes in a storm. Gutter Mesh Newcastle will also help prevent possums and vermin getting into your roof space.


All openings on the tank need mesh screens to exclude birds and small animals, and mosquitoes. These strainers need to fight tightly but should also be removable so they can be cleaned. The inlet should have a leaf litter strainer as well as a close-fitting cover to exclude mosquitoes.

One problem with fine insect mesh is that it blocks up quickly with debris and may need to be cleared constantly to be effective. If not, water can leak out and pool. Mosquitoes will breed in pooling water anywhere on the system, and eggs may wash into the tank.

If wrigglers turn up in your tap water, check that:

  • screens on all access points are in good condition
  • downpipes are in good condition and not leaking
  • guttering is clear of debris and water isn’t pooling
  • the tank isn’t damaged.

Traditionally, mosquito breeding was stopped by adding a teaspoon of domestic kerosene to the tank (don’t use power kerosene). The kerosene forms a film on the water surface, suffocating the wrigglers, and eventually evaporates. Some people advise against this, others swear by it as being cheap, simple, effective and harmless. The NSW health department recommends it.

First-flush diverters

As the name suggests, the first 20-25 litres of water off the roof are diverted away from the tank, taking everything washed off the roof with it. If you’re prepared to run out in the rain, a detachable downpipe can do the same thing, but you need to hook it up again to catch the rest of the water.

A drawback of diverters is than morning frost and dew and small amounts of rain are also diverted, causing a noticeable loss of water capture for some households. It is also another leaf filter you need to empty regularly although, depending on where you place the diverter, it may be more accessible than the strainers on the tank, and will reduce the number of times you have to check those ones.

Water filters

An inline filter on the pipe entering the house can remove any fine sediment and grit that is drawn out of the tank before it enters the lines in the house. If it’s a carbon filter, it will remove virtually all odours, too.

Chemical treatments

Chlorine is used routinely in public water supplies to overcome contamination. Chlorine compounds are also available for residential tanks and could be useful if you have problems with your water that physical methods don’t overcome. Some may require a waiting period before using the water (eg overnight treatment). Some local tank retailers carry water treatments. Get more detailed advice if you want to use chlorine in your domestic tank.


Despite all the preventive measures you adopt, sludge will build up in the tank and needs to be cleaned out periodically, perhaps every two to three years (although many people go much longer).

You need to empty the tank before you start.

With a small tank you may be able just to rinse it out with a hose (assuming an alternative water supply) and tip it on its side to drain.

A big tank is more difficult, especially if it is your only source of water.

You need to get into a big tank with a shovel, a bucket and a broom and dig the sludge out. It’s a small, confined space and can heat up quickly, so do it early in the morning and have a second person on hand to cover you if you get into difficulties, and to hand you tools, empty the bucket etc.

The following tips are obvious safety precautions: don’t use a flame or an extension cord in the tank, and be careful using chemical repair kits or petrol-driven equipment, such as a pump. The risk is real. In February 2017, at Gunning in southern NSW, a man doing routine maintenance on his tank was overtaken by fumes from a petrol pump. His brother, who went to help him, was also overtaken, as was his wife, who went to help them both. Sadly, all three perished. (See this article.)

If the tank is your only source of water and you’re not expecting rain in the afternoon, you’ll need to buy in a tanker of water to keep you going.

Desludging isn’t a job that appeals to everyone and there are commercial operators available to do it for you, including, in some areas, operators that siphon the sludge out of the tank without emptying it.

There is also a relatively new system, developed in New Zealand, that can be installed on an existing tank, even one with water in it, which claims to automatically desludge the tank floor every time the tank overflows.

Other treatments

More complicated systems, including ultraviolet (UV) treatments, distillation and reverse osmosis processes, are also available to help improve water quality. They may not kill bacteria and you should get further advice before choosing to implement such systems.

  • You can disinfect water by bringing it to a rolling boil and cooling it before drinking, a simple solution If anyone in the household is very young, very old, or has a compromised immune system and you are concerned about the water quality.
  • Don’t use water from the hot water tap for drinking or cooking (rainwater can cause corrosion in water heating systems, which passes into the water).
  • Additionally, in the morning, flush cold water taps that provide water for drinking or cooking for 2–3 minutes (water that has been standing in metal pipes can dissolve metals such as copper and lead). Use the first flush for non-drinking purposes.

And a word for RV owners … Monitoring the water quality in your RV’s water supply is more important as the risk of contaminating your water supply system is much higher.