Screens on rainwater tanks

Queensland’s Public Health Regulation 2018 deals with mosquitoes in Part 2, Division 2. It defines a “relevant tank” as a tank or other receptacle used, or intended to be used, to hold water or another liquid in which mosquitoes can breed, and gives a rainwater tank as its example.

What the tank must have, section 18

At each opening of the tank, the tank must have either:

1. a screen made of brass, copper, aluminium or stainless steel gauze, with a mesh size of not more than 1 mm, fitted so that it does not cause or speed up corrosion, and that stops mosquitoes passing through the openings; or
2. a flap valve that, when closed, stops mosquitoes passing through the opening.

A person must not construct a tank, or install one above or below ground, unless it meets those requirements. The occupier of the place, or the owner if no-one occupies it, must keep an installed tank maintained so it goes on meeting them. Each of these carries a maximum penalty of 40 penalty units.

Leaving the screen alone, section 19

Section 19 of the regulation reads: “A person must not destroy, damage or remove a mosquito-proof screen or flap valve fixed to a relevant tank.” The exception is removing it to carry out maintenance, if it is replaced immediately after the maintenance is finished. The maximum penalty is 40 penalty units.

Who enforces it

The regulation says this division is administered and enforced by local governments only, so the council is the body to ask. Queensland’s own list of household breeding sites includes checking the screens and seals on rainwater tanks.

Victoria’s Department of Health advises keeping a tank sealed, with mosquito-proof screens or flap valves, or both, on every opening, overflows included. Plastic or steel mesh can go around any pipes, valves or access points mosquitoes could get through, and inlets and overflows can be covered by a removable mesh or lid.

It puts the mesh at a gap of no more than 1–1.5 mm per hole, in brass, copper, aluminium or bronze wire, with plastic as a substitute where the mesh is removable.

Its maintenance routine has two intervals. Every three months, check the first flush diverters and look for water pooling around the tank. Every six months, check the mosquito-proof meshing for holes or defects. The department’s rainwater page adds regular checks that inlet and overflow screens are secure, in good condition and clean.

For more on meshing a tank, the department suggests a tank specialist or the local council’s environmental health unit.

NSW Health says a tank should have at least two openings, one to let rain in and an overflow, and that both should be screened against animals and mosquito breeding. Its advice is to fit every inlet and overflow with close-fitting, fine insect-proof screens, giving 1 mm as an example; to inspect them regularly, at least once a year, to make sure they stay sealed and undamaged; and to check for and repair any holes or gaps in the tank. It also asks owners to clean all screens regularly.

If prevention fails, NSW Health says the Australian Drinking Water Guidelines recommend the pesticide s-methoprene for mosquito control in rainwater tanks, and that adding kerosene or liquid paraffin is not recommended, because of possible interactions with plastic tanks or tank liners, and because they can change how the water tastes.

SA Health asks for mosquito-proof mesh over rainwater tank overflows, and says a tank or water container should either be emptied, be given a lid that seals, or have its openings covered with mosquito-proof mesh. If mosquito larvae, the “wrigglers”, are present, screen or close off the point where they got in, and don’t let water pool in containers below outlets or taps.

SA Health also describes a last-resort treatment, and on this point its advice differs from NSW Health’s above. Its procedure, in full and in our words:

1. Use it only as a last resort.
2. Ask the tank’s manufacturer whether kerosene can be used in that tank.
3. Do not add kerosene if the water level is low.
4. Use domestic kerosene or liquid paraffin only. Never put commercial or industrial kerosene, for example tractor power kerosene, in a rainwater tank.
5. The kerosene dose is 5 ml, or one teaspoon, for a 1 kilolitre tank, up to 15 ml, or three teaspoons, for a 10 kilolitre tank. For paraffin, double the dose.

In New South Wales, NSW Health’s advice is not to use kerosene or paraffin at all. Each state’s advice is its own, and the two differ here; check your own state’s health department before treating a tank.

WA Health’s advice for the home is to cover rainwater and septic tank openings, wells and other large water containers with mosquito-proof mesh. Nationally, healthdirect lists making sure rainwater tanks are sealed and inlet and outlet pipes are screened among the ways to lower mosquito numbers around a home.