BUCKHORN CLIFFS

Water · Formula · Book recipe 5.2

Purify water with calcium hypochlorite (pool shock)

Makes creek, well, rain, or other untreated water potable when boiling isn't an option. It does not remove chemical pollutants, heavy turbidity, or Cryptosporidium, a chlorine-resistant parasite that needs filtering or boiling.

HazardousWorks without power

How it works

Make stock1½ tsp / gal · ~1,000 ppm
Dose the water1 tbsp stock per gallon
Wait30 minutes
Safe to drink~2-4 ppm residual
Dilute before drinkingstock is too strong to drink straight
NEVER drink the stock or powderand never mix with acids or ammonia

Quick facts

Stock
~1,000 ppm
Dose
1 tbsp stock / gal
Wait
30 minutes
Residual
~2-4 ppm
Dry shelf life
up to 10 years

Hazard

Do not drink the stock or undiluted powder. Add powder to water; acids make toxic chlorine gas and ammonia makes toxic chloramine gas.

Calcium hypochlorite granules are one of the lightest and most cost-effective purification tools you can carry or store. You first mix a small amount of powder into water to create a concentrated stock solution, then add a measured amount of that stock to the water you want to drink. The dry granules last up to 10 years sealed, far longer than liquid bleach.

What you'll need

  • Calcium hypochlorite granules (65-70% available chlorine content, no additives or algaecides)
  • Water to be treated (well, stored supply, creek, or river)
  • Measuring spoons (1 teaspoon and 1 tablespoon)
  • Non-metallic container with sealable lid (glass jar or HDPE jug)
  • Non-metallic stirring tool (plastic or wooden)

Steps

  1. Pre-filter cloudy or suspect water through a clean cloth, or a bottle filter (Recipe 7.3), to remove sediment. Clear water can skip this step
  2. Make a stock solution by mixing 1½ level teaspoons (about 5.7 to 6 grams) of calcium hypochlorite granules into 1 gallon of water and stirring until dissolved. This stock is ~1,000 ppm, too strong to drink directly. Use within 24 hours
  3. Treat the drinking water by adding 1 tablespoon of stock solution per gallon. For cloudy or suspect water, use 2 tablespoons per gallon. Stir well
  4. Wait 30 minutes before drinking (60 minutes for cloudy water). A faint chlorine smell at the end confirms residual chlorine. If no smell, add another tablespoon and wait 30 more minutes
  5. To cut the chlorine taste in water you will drink soon, aerate it by pouring back and forth between two clean containers, or stir in a small pinch of ascorbic acid (vitamin C) per gallon

Warnings

Don't drink the stock solution or undiluted powder. Always add powder to water, never the reverse, to avoid violent reactions and gas release. Wear chemical-resistant gloves and eye protection. Work in well-ventilated areas. If you smell strong chlorine or experience coughing or throat irritation, move to fresh air immediately. Keep dry powder away from fuels, oils, and combustible materials. Keep away from children and pets.

Storage and shelf life

Sealed dry powder: up to 10 years cool, dry, dark. Stock solution: use within 24 hours. Treated drinking water: replace every 6 months in sealed, opaque containers in a cool, dark place. Best container: sealed glass jar or HDPE jug. Avoid metal. See the Containers section.

Questions this answers

Tap a question for the short answer.

How do I purify water with pool shock?

Pre-filter cloudy water, then make a stock solution of 1½ level teaspoons of calcium hypochlorite granules in 1 gallon of water. Add 1 tablespoon of that stock per gallon of drinking water, or 2 tablespoons if cloudy, stir, and wait 30 minutes. Never drink the stock itself.

How much calcium hypochlorite do I use per gallon of water?

Two steps. The stock solution takes 1½ level teaspoons of granules, about 5.7 to 6 grams, per 1 gallon of water. Then dose drinking water with 1 tablespoon of stock per gallon, or 2 tablespoons per gallon for cloudy or suspect water.

How long does pool shock last in storage?

Sealed dry powder lasts up to 10 years when kept cool, dry, and dark, far longer than liquid bleach. Once mixed, the stock solution must be used within 24 hours, and treated drinking water should be replaced every 6 months.

How long do I wait before drinking chlorinated water?

Wait 30 minutes for clear water and 60 minutes for cloudy water. A faint chlorine smell at the end confirms residual chlorine. If you smell nothing, add another tablespoon of stock and wait 30 more minutes.

How do I get rid of the chlorine taste in treated water?

Aerate the water by pouring it back and forth between two clean containers, or stir in a small pinch of ascorbic acid (vitamin C) per gallon. Do this for water you plan to drink soon.

What kind of pool shock is safe for drinking water?

Choose calcium hypochlorite granules with 65 to 70% available chlorine and no additives or algaecides. Mix and store it in non-metallic containers such as a glass jar or HDPE jug, and stir with a plastic or wooden tool.

Keep going

Read nextWater purification methodsAn overview of making water safe: calcium hypochlorite treatment, well water risks, water testing tools, and what to do when city water is cut off.Water · Guide

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