How to Bleach Bacteria in Cistern Water

Cistern water, which is often collected for watering a garden in order to conserve drinking water, can be converted to drinking water in times of an emergency by adding the appropriate concentration of bleach to the water. The bleach is only effective, however, if your cistern is properly cleaned on a consistent basis and it has the appropriate cover that will keep out insects, foreign matter, and contaminated run-off water. The disinfected water may be used for cooking, bathing, washing dishes and for human consumption.

Disinfect cistern water

  1. Check to see that the cistern has been properly cleaned in advance and that it has been covered properly. (For more information, see warnings below.)

  2. Add 2 drops of bleach per gallon, or 3 fluid ounces of bleach per 1,000 gallons.

  3. Wait five minutes before using the water.


  • Using bleach to disinfect cistern water is only effective if you make sure to clean your cistern at least once a year before the rainy season. This will reduce the presence of microorganisms. Do this by draining any water out of the cistern. Scrub down the walls of the cistern with a mixture of water and bleach, approximately 1/4 cup bleach per 10 gallons of water. Make sure the cistern is properly ventilated during this process so that you are not overcome with fumes. Then rinse the cistern until you no longer smell bleach.
  • Regularly check for cracks and other defects in the walls and cover of your cistern.
  • In addition, make sure that your cistern is properly covered. Cistern covers should be made of durable, nonporous material and should fit tightly to prevent insects and foreign matter from getting inside. The cover should also be surrounded with an air tight lip to keep out contaminated run-off water. The University of Kentucky says that cistern water is only as clean as the cistern itself and the water that goes in it.