Ask most Bangalore homeowners when they last cleaned their overhead tank or sump and you'll get a shrug, a guess, or "the builder did it before we moved in." That's usually three, five, sometimes ten years ago. The water still comes out of the tap looking clear, so nobody worries. That's exactly the problem — a contaminated tank rarely announces itself. It just quietly supplies your kitchen and bathroom while doing damage you can't see.
What BWSSB and health authorities actually recommend
The guidance is specific, not vague. If your tank is fed by borewell or tanker water, clean it every 3 months — both sources carry more sediment and bacterial load than treated Cauvery supply. If you're on BWSSB piped water only, 6 months is the outer limit. Add one extra cleaning right after monsoon, when runoff, silt and organic debris spike contamination regardless of source. Health department advisories for domestic and apartment tanks converge on the same window: 3–6 months, not once a year, and never "whenever we remember."
Reality check: If your tank hasn't been opened in over a year, you're not slightly overdue. You're storing and drinking from a system that's had 2–4x the recommended contamination-building time to do its work.
What actually grows in a tank left too long
This isn't hypothetical grime — it's a specific, predictable buildup:
None of this requires the water to look, smell, or taste different at first. Biofilm and early algae growth are essentially invisible from the outside — you'd have to open the tank and look at the walls to catch it early.
Visible signs vs. what's already gone too far
By the time you notice these, the contamination has usually been building for months already:
- Visible: yellow or brownish tint to the water, a musty or sulphur-like smell, slimy residue on bucket edges or the tank lid, visibly floating debris.
- Invisible until it's advanced: bacterial contamination that doesn't change colour or smell, mosquito larvae hiding below the visible waterline, sediment settled at the base that only stirs up during heavy usage.
Waiting for a visible sign before you act means you've already been drinking and bathing in the invisible stage for weeks or months.
Higher-risk households: young children, elderly family members, and anyone with a compromised immune system are more exposed to the same contamination that a healthy adult might shrug off. If that's your household, don't stretch the cleaning interval.
A quick rinse is not a cleaning
A lot of what passes for "tank cleaning" in Bangalore is a plumber draining the tank, hosing the inside for two minutes, and refilling it. That removes loose floating debris and nothing else. The biofilm coating the walls stays. The sediment layer at the base gets disturbed, not removed. A proper cleaning looks different: complete draining, manual scrubbing of every interior wall, floor and corner, a high-pressure jet wash to flush loosened debris out through the drain (not back into the tank), a food-safe anti-bacterial treatment applied to kill what scrubbing missed, and a rinse-refill with a TDS check before you start using it again. If your last "cleaning" took under 20 minutes and nobody physically entered or scrubbed the tank, it was a rinse.
What it actually costs
| Tank Type | Size | Price Range |
|---|---|---|
| Overhead tank (small) | Up to 1,000L | ₹749–₹1,200 |
| Overhead tank (medium) | 1,000–2,000L | ₹1,200–₹1,800 |
| Underground sump (small) | Up to 5,000L | ₹1,500–₹2,500 |
| Underground sump (large) | 5,000–10,000L | ₹2,500–₹4,000 |
| Apartment society tank | 10,000L+ | Custom quote |
An Annual Maintenance Contract works out cheaper per visit — 2–4 scheduled cleanings a year at a discount, with reminders so you're not relying on memory. For a single household on borewell water, budget roughly ₹3,000–₹6,000 a year for proper coverage. That's a small number against a family's drinking water.
Book it this week, not "sometime"
If you can't remember your last cleaning, don't wait for a visible sign — book the inspection now. We check tank condition on the spot, tell you straight whether you need a cleaning or it can wait, and if it needs doing, we do it the same week. No quote-shopping detour required.
Frequently asked questions
Every 3 months if you use borewell or tanker water, and every 6 months if you're on BWSSB Cauvery supply only. Add one extra cleaning right after monsoon regardless of source.
Algae along the waterline, sediment at the base, mosquito larvae near the inlet, and bacterial biofilm — including E. coli and Salmonella — on the tank walls. None of it needs the water to look dirty.
No. A rinse just drains and refills without removing biofilm or base sediment. A proper cleaning scrubs every surface, jet-washes debris out, and applies anti-bacterial treatment before refilling.
₹749–₹1,800 for an overhead tank up to 2,000L, and ₹1,500–₹4,000 for an underground sump depending on size. Free inspection available first.