Used to sanitize storage containers before filling them with clean drinking water for long-term storage or use in off-grid situations
Calcium hypochlorite (commonly sold as “pool shock”) can be used to sanitize water barrels, rain collection tanks, and cisterns. Disinfecting these containers before use helps prevent microbial growth, biofilm buildup, and contamination. This method is simple, effective, and ideal for anyone storing water long-term.
Ingredients:
- Calcium hypochlorite (granular, 65–70% available chlorine; no additives or algaecides)
- Water from a freshwater source (creek, river, well, or stored supply)
- Measuring spoons (1 heaping teaspoon, ¾ cup)
- Non-metallic container (HDPE jug or glass jar with gasket lid)
- Non-metallic stirring utensil (plastic or wood)
- Spray bottle, sponge, or bucket (optional, for cleaning interior walls)
How to Make It:
- Make a stock solution by dissolving 1 heaping teaspoon (about 7 grams) of calcium hypochlorite into 1 gallon of water. Stir until fully dissolved. This creates a concentrated chlorine solution for disinfecting containers.
- To clean a 55-gallon water barrel or cistern, add ¾ cup of this stock solution to the container, then fill with water. You don’t have to fill the entire barrel—just ensure all interior surfaces are coated by rotating, spraying, or wiping with the disinfecting solution. Stir, shake, or roll the barrel to coat all interior surfaces. Let sit for at least 30 minutes, then drain and rinse with clean water before refilling with potable water.
- For a deeper clean, using half a gallon of stock solution in a 55-gallon barrel creates a stronger mix (~200 ppm) for heavy-duty sanitizing; rinse thoroughly afterward before filling with drinking water.
- For spraying or wiping interior surfaces, apply the full-strength solution directly using a spray bottle, sponge, or cloth. Allow to sit for 30 minutes, then rinse thoroughly.
Warnings:
- Do not drink water directly from a container that has been cleaned but not rinsed.
- Always add powder to water, never water to powder — adding water to dry calcium hypochlorite can cause a rapid, dangerous reaction or release of heat and gas. Mixing the other way is safer and controlled.
- Use in a ventilated area and wear gloves and eye protection.
- Keep out of reach of children and pets.
Storage & Shelf Life:
- Dry calcium hypochlorite: Use to make container-cleaning solution; shelf life 10+ years when kept completely dry.
- Prepared sanitizing solution (7 grams in 1 gallon): Use for container disinfection; shelf life 24–48 hours.