📖 How To Use
How to Use This Calculator
Getting the correct bleach dose takes under a minute:
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Select your use type
Choose "Drinking Water" for potable water treatment, "Tank Disinfection" for cleaning storage tanks, or "Surface Sanitation" for disinfecting food-contact surfaces. Each use case requires a different chlorine concentration.
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Enter your water volume
Enter the total volume of water you need to treat. Use litres, US gallons, UK gallons, millilitres, or cubic metres — select the unit that matches your container or tank label.
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Enter your bleach concentration
Check the label on your bleach bottle. Standard household bleach is 5.25% or 8.25% sodium hypochlorite. Use the quick-set buttons for the most common strengths.
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Read your result
The calculator shows the exact bleach volume to add in ml, fluid ounces, drops, and teaspoons. For small volumes, use drops for precision; for large tanks, use ml.
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Mix and wait
Add the measured bleach to the water and stir. For drinking water, wait at least 30 minutes before consuming. A faint chlorine smell is normal and confirms disinfection.
Important: This calculator assumes clear, room-temperature water. Turbid or cold water requires double the dose. If water is cloudy, filter it through a cloth first, then treat. Always verify with a chlorine test strip if treating water for vulnerable populations.
📐 The Formula
Bleach to Water Ratio Formula
The dosage is calculated from the required chlorine concentration and your bleach's sodium hypochlorite content:
Bleach Volume (ml) = (Target Dose mg/L × Water Volume L) ÷ (Bleach % × 10)
Where: Bleach % × 10 = mg/ml of available chlorine
Example (drinking water, 5.25% bleach, 100 L):
= (2 mg/L × 100 L) ÷ (5.25 × 10) = 200 ÷ 52.5 = 3.81 ml
This calculator applies the WHO and CDC recommended chlorine dose targets for each use case, then back-calculates the bleach volume from your bottle's concentration.
Target Chlorine Doses by Use
| Use Type | Target Free Chlorine | Source | Contact Time |
|---|
| Drinking Water (clear) | 2 mg/L (ppm) | WHO/CDC | 30 min |
| Drinking Water (turbid) | 4 mg/L (ppm) | WHO/CDC | 60 min |
| Tank Disinfection | 50 mg/L (ppm) | NSF/AWWA | 12–24 hr |
| Surface Sanitation | 200 mg/L (ppm) | CDC/EPA | 10 min |
Common Bleach Quick Reference
| Use / Volume | 3.5% Bleach | 5.25% Bleach | 8.25% Bleach |
|---|
| Drinking: 1 L | 0.57 ml | 0.38 ml | 0.24 ml |
| Drinking: 20 L | 11.4 ml | 7.6 ml | 4.8 ml |
| Drinking: 100 L | 57 ml | 38 ml | 24 ml |
| Tank: 1,000 L | 1,429 ml | 952 ml | 606 ml |
| Tank: 5,000 L | 7,143 ml | 4,762 ml | 3,030 ml |
💡 Use Cases
When to Disinfect Water with Bleach
🚨
Emergency / Disaster
Floods, pipe failures, and boil-water advisories can contaminate tap water. Chlorination is the fastest reliable method when clean water access is interrupted.
🛢️
New or Cleaned Tanks
Before first use and after any repair or cleaning, storage tanks must be disinfected. Biofilm and bacteria establish within 24 hours in untreated water.
🏕️
Off-Grid & Camping
River, rainwater, and borehole water may carry pathogens. Bleach treatment is lightweight, cheap, and effective against bacteria and most viruses.
🌿
Agricultural Irrigation
Livestock water troughs and irrigation systems require periodic disinfection to prevent bacterial contamination that can affect animal health and crop safety.
What Bleach Does (and Doesn't) Kill
Sodium hypochlorite at the recommended doses is effective against bacteria (E. coli, Salmonella, Vibrio cholerae), most viruses (including hepatitis A, norovirus), and many protozoan cysts. It is not effective against Cryptosporidium without extended contact times at very high doses — for water suspected of Cryptosporidium contamination, use a 1-micron filter or boiling instead.
❓ FAQ
Frequently Asked Questions
What is the bleach to water ratio for drinking water?
For clear drinking water using standard 5.25% household bleach, the ratio is approximately 2 drops (0.1 ml) per litre of water, or 8 drops per US gallon. For larger volumes, use this calculator to get exact millilitre measurements. Wait 30 minutes before drinking and verify a faint chlorine smell remains.
Can I use any bleach for water treatment?
Only use unscented sodium hypochlorite bleach with no added thickeners or surfactants. Scented bleach, gel bleach, or bleach marketed for laundry with added fragrances should never be used for drinking water. Always check the label — it must list sodium hypochlorite as the only active ingredient.
How much bleach do I need to disinfect a 1,000 litre water tank?
For tank disinfection (50 mg/L target), using 5.25% bleach: approximately 952 ml (just under 1 litre) of bleach per 1,000 litres of water. Fill the tank, add the bleach, circulate if possible, and leave for 12–24 hours. Then drain, rinse, and refill with fresh water.
How do I know if I've added too much bleach?
Over-chlorinated water has a strong, sharp chlorine smell and may cause throat irritation. The treated water is still safe — just aerate it by pouring between containers repeatedly or letting it stand uncovered for several hours. The excess chlorine will dissipate. Use a chlorine test strip to confirm the level has dropped to under 4 mg/L before drinking.
Does bleach expire? Does old bleach still work?
Yes. Sodium hypochlorite degrades over time — typically losing 20% potency per year when stored at room temperature. Bleach more than a year old should not be used for water treatment unless the concentration can be verified. Store bleach in a cool, dark place and replace annually for emergency preparedness kits.
How long does chlorinated water stay safe?
Properly chlorinated water stored in a sealed, clean container in a cool location remains safe for up to 6 months. If stored in a container that has been opened or exposed to sunlight, residual chlorine dissipates faster — retest or re-treat every 3 months. Use our Safe Water Storage Duration Calculator for precise estimates.
What is the difference between chlorine dosage for drinking water vs. tank disinfection?
Drinking water treatment targets 2 mg/L — just enough to kill pathogens while remaining safe to consume. Tank disinfection requires 50 mg/L — 25 times higher — to kill bacteria embedded in biofilm on tank walls. This is a shock treatment: the water must be drained after disinfection and is not drinkable at tank disinfection concentrations.
Is there a calculator for chlorine dosage specifically?
Yes — our dedicated Chlorine Dosage Calculator allows custom mg/L target inputs for precise water treatment applications, including pool treatment and industrial water systems. The bleach-to-water calculator you're using now is designed for household and emergency use with preset WHO/CDC dose targets.