Keeping mosquitoes out of your water tank comes down to four things: mosquito-proof screens on every opening, a flap valve on the overflow, a properly sealed lid, and a quick inspection every few months. Get those right, and your tank stays a water supply — not a breeding ground.
It sounds simple, and for the most part it is. The catch? Most tank owners set everything up correctly on day one, then never look at those screens again. Meanwhile, sun, storms and the odd curious possum slowly undo the good work. With spring on the way, late winter is exactly the right time for a check-up.
So grab a cuppa, and let’s walk through how mosquitoes get in, what the rules actually require, and the five entry points worth checking on your own tank this weekend.
Why Mosquitoes Love Water Tanks
A rainwater tank offers everything a mosquito could want: still water, shade, protection from wind and predators, and a stable temperature. Female mosquitoes lay their eggs on or near standing water, and larvae — those little “wrigglers” you might have spotted in a bucket or birdbath — develop in as little as a week during warm weather.
Here’s the part that matters for your household. Mosquitoes in Australia can carry Ross River virus and Barmah Forest virus, and in parts of North Queensland, dengue as well. Your state health department publishes current advice on mosquito-borne disease, and it’s worth a read if you live in a warmer region.
An unscreened tank doesn’t just breed a few mozzies for your backyard barbecue, either. It can supply an entire neighbourhood. That’s why every Australian state treats tank screening as a requirement, not a suggestion.
What the Rules Say
Australian guidelines require rainwater tanks to be mosquito-proofed. In practice, that means:
- All openings screened with mesh no coarser than 1mm aperture — fine enough that adult mosquitoes can’t get through
- Overflow outlets fitted with a flap valve or removable screen
- Lids and access points properly sealed, with no gaps around fittings
- Screens made from durable material — brass, copper, aluminium or stainless steel gauze holds up far better than plastic mesh in Australian sun
The good news is that a quality poly tank arrives with all of this built in. Every tank we manufacture ships with a mosquito-proof inlet strainer and screened overflow as standard. The screening rules only become a problem when components age, get damaged, or go missing after maintenance.
The Five Entry Points Worth Checking
Mosquitoes only need a gap of a couple of millimetres. Consequently, a “screened” tank with one small fault is no better than an unscreened one. Here’s where to look.
1. The Inlet Strainer
This is the basket-style screen where water enters from your downpipes. Check the mesh for tears, holes and gaps around the rim. Above all, make sure it’s actually sitting in place — strainers often get set aside during gutter cleaning and never quite make it back.
2. The Overflow Outlet
The most commonly forgotten entry point on any tank. When your tank overflows, water exits through this pipe — and when it’s not overflowing, mosquitoes can fly straight up it. A flap valve or screened outlet fixes the problem. If your overflow runs to a drain, check the screen hasn’t rusted or fallen off at the tank end.
3. Air Vents
Tanks need to breathe as water levels rise and fall. Those vents must be screened too. Give them a look while you’re up there.
4. The Lid and Access Hatch
Check that the lid seats properly and hasn’t warped or cracked. After any maintenance or cleaning, confirm it’s been closed correctly — a lid left ajar is an open invitation.
5. Fittings and Joins
Finally, run your eye over every point where something enters or exits the tank: pump lines, level indicators, interconnecting pipes between linked tanks. Gaps around fittings are small, but they’re plenty big enough for a mosquito.
Your Twice-a-Year Screen Check
A full check takes about ten minutes. Do it twice a year — once in late winter before mosquito season ramps up, and once in autumn. It fits neatly alongside the routine in our water tank care guide, so you can knock both over in one go.
1. Inspect the inlet strainer for damage and correct seating
2. Check the overflow flap valve or screen moves freely and seals shut
3. Confirm all vents are screened and intact
4. Check the lid seal and access hatch
5. Look over every fitting for gaps
6. Clear leaves and debris from the tank top and gutters — organic matter attracts egg-laying females
2. Check the overflow flap valve or screen moves freely and seals shut
3. Confirm all vents are screened and intact
4. Check the lid seal and access hatch
5. Look over every fitting for gaps
6. Clear leaves and debris from the tank top and gutters — organic matter attracts egg-laying females
Replacement strainers, screens and flap valves are inexpensive and easy to fit yourself. You’ll find them among our tank accessories, and if you’re not sure which part suits your tank, give us a call on 1300 826 532.
Already Got Wrigglers? Here’s What to Do
Found larvae in your tank water? Don’t panic, and don’t tip the whole tank out. First, find and fix the entry point — otherwise you’ll be back here in a fortnight. Once the tank is sealed, the existing larvae can’t complete their life cycle and escape as adults.
If you drink your tank water, it’s sensible to check water quality afterwards. Our guide on whether you can drink tank water covers filtration and treatment options in plain English. For a heavily affected tank, a clean-out and fresh start may be worth it — especially if the water smells off or shows visible contamination.
One thing to avoid: pouring kerosene or oil into a drinking-water tank, an old bush trick you’ll still hear about. It contaminates your supply and isn’t necessary once the tank is properly sealed.
Frequently Asked Questions: Mosquitoes in Water Tanks
Can mosquitoes breed inside a sealed water tank?
No — a properly sealed tank with intact screens on every opening gives mosquitoes no way in. Breeding only happens when there’s a gap: a torn inlet strainer, an unscreened overflow, or a lid that doesn’t seat properly. That’s why regular screen checks matter more than any treatment.
What size mesh keeps mosquitoes out of a rainwater tank?
Mesh with an aperture of 1mm or finer will stop adult mosquitoes. Metal gauze — brass, aluminium or stainless steel — lasts far longer than plastic mesh under Australian UV. All new tanks from The Water Tank Factory include compliant mosquito-proof screens as standard.
Are mosquito larvae in tank water dangerous to drink?
Larvae themselves aren’t a major health risk if accidentally swallowed, but their presence tells you the tank is open to contamination from other sources too. Fix the entry point, then assess water quality. If in doubt, boil or filter drinking water until the tank has been checked.
How often should I check my tank screens?
Twice a year is the sweet spot — late winter and autumn. Add an extra check after major storms, gutter cleaning, or any tank maintenance, because that’s when strainers and lids most often get dislodged.
Give Your Tank a Once-Over Before the Weather Warms Up
Ten minutes with a ladder now beats a summer of slapping mozzies later. Check your screens, fit a flap valve if your overflow doesn’t have one, and your tank will keep doing what it does best — storing clean, safe water for your home.
Need replacement strainers, screens or accessories? The Water Tank Factory — the online sales division of Duraplas Industries — has been manufacturing tanks since 1984 in Alstonville, Northern Rivers NSW, with over 250,000 tanks manufactured. Browse the range at www.watertankfactory.com.au or call the team on 1300 826 532.