Interactive Calculator · 2026
Water Tank Chlorination Calculator
Work out how much household bleach disinfects a drinking-water storage tank. Enter the tank volume, the target chlorine dose and the bleach strength — get the chlorine required, the bleach quantity to add and a suggested contact time before you flush and refill.
Bleach required across common tank sizes (your tank highlighted)
Your tank & dose
Total water the tank holds when full — a typical overhead tank is 500–2,000 L.
A shock dose for cleaning a tank (2–5 mg/L) is higher than the ~0.2–0.5 mg/L residual left in tap water. Higher doses need thorough flushing before use.
Household bleach (sodium hypochlorite) is usually 4–6% available chlorine — check the label, as it weakens with age.
Bleach required across tank sizes
At your dose (2 mg/L) and bleach strength (5%) — bigger tanks need proportionally more bleach.
For your 1,000 L tank at a 2 mg/L shock dose, add about 40 mL of 5% bleach — that delivers 2 g of available chlorine.
Leave it in contact for at least 30 minutes, then drain, flush thoroughly and refill before the water is used.
How this is calculated
- Chlorine required = volume × dose = 1,000 L × 2 mg/L = 2,000 mg = 2 g of available chlorine.
- Bleach quantity = chlorine required ÷ (strength × 1000) = 2,000 ÷ (0.050 × 1000) = 40 mL. As a rule of thumb, 1 mL of 5% bleach carries about 50 mg of available chlorine.
- Suggested contact time = 30 min — at least ~30 minutes for a full-strength shock dose, longer for lighter doses, before draining and flushing.
Indicative dosing for periodic tank disinfection and cleaning — not for continuous drinking-water dosing. Ventilate the area, wear gloves, and never mix bleach with other cleaners (it releases toxic gas). After the contact time, drain and flush thoroughly and confirm the residual chlorine has fallen to a safe level (typically ≤0.5 mg/L) before use. Verify potability by testing. This is not medical or regulatory advice — confirm with a qualified professional and your local water authority.
Frequently asked questions
- How does the water tank chlorination calculator work?
- It works out the shock dose of household bleach needed to disinfect a storage tank. Chlorine required equals tank volume multiplied by the target dose, so a 1,000 litre tank at 2 mg/L needs about 2 grams of available chlorine. Bleach quantity is that chlorine divided by the bleach strength — roughly 1 mL of 5 percent bleach carries about 50 mg of available chlorine.
- What inputs and values should I use?
- Enter the tank volume in litres (a typical overhead tank is 500 to 2,000 L), a target chlorine dose, and the bleach strength. For periodic cleaning a shock dose of 2 to 5 mg/L is common, far higher than the 0.2 to 0.5 mg/L residual left in tap water. Household bleach is usually 4 to 6 percent available chlorine, but check the label since it weakens with age.
- How long should the chlorine stay in contact, and what must I verify?
- Leave the dosed water in contact for at least 30 minutes, longer for lighter doses, then drain, flush thoroughly and refill before use. Confirm the residual chlorine has fallen to a safe level, typically at or below 0.5 mg/L, and test potability before drinking. Ventilate the area, wear gloves, and never mix bleach with other cleaners. These figures are indicative for planning; verify locally with your water authority or a qualified professional. This is not medical advice.
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