Mosquito-Proofing Overhead Tanks and Sumps

Overhead tanks and sumps hold large amounts of water, and an open or poorly sealed one can become a major mosquito breeding site. Gaps in lids, open vent pipes and overflow outlets all give mosquitoes a way in, and thousands can emerge from a single neglected tank.

This guide explains how to keep them out.

The short answer

To mosquito-proof overhead tanks and sumps, fit tight, well-fitting lids with no gaps, cover vent pipes and overflow outlets with fine mesh, repair cracks and broken covers, keep inspection hatches closed and sealed, clean the tank and sump regularly, check for larvae and tiny gaps during each cleaning, and keep the surrounding area dry and clear. Mosquitoes can enter through very small openings, so use fine, durable mesh. Societies should include tanks and sumps in routine inspection.

Why tanks breed mosquitoes

• Large volume of standing water, often undisturbed.
• Gaps in lids and covers, open vents and overflow pipes.
• Poor maintenance and infrequent cleaning.
• Dirt and sediment at the bottom provide food for larvae.

Where mosquitoes get in

1. Gaps around lids and manholes.
2. Open air vent pipes.
3. Overflow and washout pipe outlets.
4. Cracks in the tank body or cover.
5. Broken inspection hatches.

How to mosquito-proof

• Lids: Use tight-fitting lids, in good repair, and keep them closed.
• Mesh on vents and overflows: Use fine mesh, about the density of a mosquito net, secured firmly. Use rust-resistant material.
• Seal gaps: Close cracks and gaps in covers and around pipes.
• Inspection hatches: Keep them closed and sealed.
• Surroundings: Keep the terrace and sump area dry and free of puddles.

Cleaning and checking

1. Clean tanks and sumps regularly, as advised for your area, typically every few months.
2. During cleaning, look for larvae, pupae and dead insects.
3. Check mesh, lids and seals for damage after each cleaning.
4. Use a torch to check the water surface during inspection.

If you find larvae

• Clean and disinfect the tank properly before it is used again.
• Fix the entry points.
• For drinking water tanks, do not use insecticides directly. Ask a professional or the water authority for safe measures.

Sumps and underground tanks

Underground sumps can be harder to inspect. Make sure covers are sealed and vents are screened, and arrange periodic inspection and cleaning.

For societies

• Include tanks and sumps in the maintenance schedule.
• Keep records of cleaning and inspections.
• Ask residents to report open or damaged lids.

Safety

Be careful when working on terraces and tank roofs. Use trained people, and do not enter tanks without proper safety measures.

When to call a professional

A tank cleaning service can clean and inspect safely, and a pest control provider can advise on breeding control without contaminating the water.

Frequently asked questions

How fine should the mesh be?

Fine enough to stop mosquitoes, like mosquito netting.

Can mosquitoes breed in clean drinking water tanks?

Yes, if they can get in.

How often should tanks be cleaned?

Regularly, as advised locally, and more often if you find problems.

Can I add chemicals to the tank?

Do not add insecticides to drinking water. Seek proper advice.

This guide is part of IPest's complete resource on mosquito control. For identification help, prevention and treatment options, see our full mosquito control guide for Bangalore.