The tank is the reason the kettle tastes fine: the annual scrub, done in the right order

Every stored-water complaint the kitchen notices - the flat taste, the silt that meets the pump when pressure dips, the film that skates across the bucket - was living in the tank first, quietly building for months. Roof tanks are not set-and-forget plumbing; they are open vessels that turn borehole or mains water into a held inventory, and held water asks three questions every year: what settled, what grew, and what got in. This page is the honest maintenance calendar, from the lid to the last rinse, with the two numbers the treatment plan runs on.

The real schedule, set by the source not the calendar

The desk's working line: every household with a tank opens it for inspection once a year, and the ones that need the full clean twice a year are identifiable from the lid alone - a borehole that carries silt (the orange stain of iron, the fine sand that never fully settles out), a roof-fed or 'make-up' line drawing from a questionable source, or a tank whose vent mesh is last season's engineering. Mains-water-only houses in good areas are the lucky exception that can go longer between scrubs and never between inspections. The sign that the schedule missed: after a pump shutdown, the first draw is cloudy or gritty - that is the settled bed being stirred, and the tank is overdue, full stop.

The clean, in the order the water cooperates

1. Plan the drain: a tank full of dirty water needs somewhere honest to go - the garden line, not the kitchen taps' own suction. Close the outlet, run the level down or pump it out to what the scrub needs.
2. Enter right or don't enter: the desk prints the safety line plainly - a sealed tank is an confined space: no ladder-in-and-hold-your-breath descents, no candles to 'test the air'; a scrub from the hatch with a long-handled brush reaches the silt that matters, and a real internal scrub of a big tank is a paid job with someone holding the ladder and the lid open. Chlorine fumes and a closed roof in the sun are the reason this paragraph exists.
3. Scrub, don't just rinse: the biofilm clings - the walls' slick and the lid's underside are the two surfaces the bucket-and-hose routine skips and the brush never should. No detergents, no 'tank cleaner' chemicals: the water you will drink is the only test that counts, and soap is the one thing the tank must never taste.
4. Drain, rinse, refill, and the first draw goes to the garden - not the kettle - until the water runs clear and the smell is just water.

Chlorine: the one number, and why the shop's advice is wrong

Shock treatment is dosing known-strength chlorine into a known volume and letting contact time do the work - the honest version of the household's 'some bleach' habit is that it is a measurement, not a pour: the tank's litres are maths from its diameter and depth, the product label states its percentage, and the safe drinking-water target the public-health guidance repeats is a small, measurable residual after the contact time - which means too little is theatre and too much is a chemical tasting party with your kettle as the judge. The desk's practical route for a household: use the local water authority's or a public-health leaflet's dosing table for your exact product and volume, keep a copy with the chlorine, and after a shock, the tank refills with fresh and the first draws are tested before the drinking line reopens. And the truth the sellers omit: chlorine kills what swims, does nothing about the silt bed or the iron - a tank that needs scrubbing every year may need the borehole's sediment stage checked (the water-treatment guide names the filters that belong to that fight).

The lid: half the annual job, ninety percent of the prevention

Everything the scrub removes gets in through a gap: the mesh on the vents that mosquitoes and leaf-fall shred, the lid seal that a brick 'to keep it closed' has warped, the overflow pipe that was cut short and open when it should wear a meshed bend, the float valve whose seat ages and drips the level down into an air gap nothing was designed for. The annual inspection's checklist is the lid's: closed flush, screened at every opening, no light inside (light grows the green), and the tank's own stand clear of the ground the pump splash soaks. A tank that is sealed and dark needs a fraction of the scrubbing of one that is not - the free half of this page.

The desk's standing rule

Inspect every year at the start of the rains, scrub when the floor of the tank says so, dose chlorine as a measurement from a label and not a mood, and treat the lid like the tank's front door - because every contaminant this guide lists has a lid story, and every clean tank this desk has opened with a happy owner had one thing in common: someone who checked the lid in March.