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Public Health - Seattle & King County

How to prepare safe water after a disaster

How does water become contaminated in a disaster situation?
  • A disaster such as a flood or an earthquake may contaminate water when sewage systems are damaged or when there are breaks in the water lines.
  • Contaminated water can cause many illnesses.
  • It is best to have a supply of water on hand to prepare for these times; however, this fact sheet will help you if you did not plan ahead, and you need to find purified water now.
How will I know if my water has been contaminated?
  • When it is suspected that water supplies have been contaminated with sewage, there will be a public announcement to boil the water. This is known as a "boil water order."
  • If there is any chance of your water being contaminated, do not drink it or use it for food preparation or tooth brushing.
How can I identify purified water?
  • Purified water can be prepared by anyone at home, or it can be purchased. Instructions are provided below on how to purify water at home.
  • Canned drinks, such as juices, pop, or beer can be considered purified.
  • Boiling water kills bacteria, viruses, and parasites that can cause illness. Treating water with chlorine bleach kills most disease causing bacteria and viruses; however it probably will not kill parasites. Boiling is a more effective water purification method than treating water with chlorine bleach.
  • People who have weakened immune systems and who are in an area where the water has been contaminated should always rely on boiling as their home water purification method, or they should buy distilled bottled water or canned drinks.
  • Use purified water within six months of its purification or purchase date to assure safety and obtain the best quality.
How do I boil water to purify it?
  • Fill a large pot with water after straining the water through a coffee filter or cheesecloth to remove dirt and other particles.
  • Bring the water to a rolling boil and keep it boiling for 1 minute.
  • Pour the water into a disinfected drinking water bottle.
  • Store in the refrigerator, if possible.
How do I use chlorine bleach to purify water?
  • Strain the water through a coffee filter or cheesecloth to remove dirt and other particles.
  • It is easiest to use gallon size drinking water containers to calculate the correct chlorine bleach solution.
  • Pour a mixture of 1/8 teaspoon or 16 drops of pure, unscented, household chlorine bleach into the gallon size, purified drinking water container. Let this stand at least 30 minutes without drinking the water.
  • If the water is still cloudy after 30 minutes, you may add an additional 1/8 teaspoon or 16 drops of chlorine bleach to the gallon size container. Let the water stand another 30 minutes.
  • If the water is still cloudy after the second treatment do not drink the water.
  • CAUTION: Do not use more chlorine bleach than recommended because excessive amounts can be poisonous!
What are the best types of containers to use to store water?
  • Use clean plastic or glass containers such as soft drink bottles or canning jars that have tight fitting screw caps.
  • Do not use milk bottles - they do not seal well.
  • Water containers should be disinfected before filling them with purified water the first time and disinfected again each time they are refilled.
How do I disinfect a drinking water container?
  • Containers can be purified either by using bleach as a chemical disinfectant or by boiling the container.
  • Plastic containers cannot be boiled.
  • Before using either method provided below to disinfect a container, wash the container thoroughly with soap and water, and rinse out the container with water.
How do I use bleach to disinfect a water container?
  • Pour a solution of 1 tablespoon of liquid household bleach to a gallon of water into the container.
  • Let the solution remain in the container for 10 minutes, then pour out the solution.
  • Rinse the container with purified water. Pour out the rinse water.
  • Fill the container again with purified water, then cap the container for later use.
  • Use the stored water within six months.
How do I boil a water container to disinfect it?
  • You may boil glass bottles or jars to disinfect them.
  • In a large pan submerge the glass bottle or jar in water.
  • Bring to a rolling boil and then boil the container for 10 minutes.
  • Fill the glass bottles and jars with purified water and cap the container for later use.
  • Use the stored water within six months.
What if I prefer to buy my drinking water?
  • There are many waters available for purchase.
  • Keep the water in its original sealed container until you plan to drink it.
  • Use the water after the container is open. Do not store it further.
  • Commercially canned or bottled drinks are always considered safe to drink.
Can I depend on water treatment devices to purify water adequately in these situations?

NO. Most home water treatment systems have not been designed to treat turbid, contaminated drinking water. The filter can become clogged quickly reducing fixture output or overloading the filter, and providing no protection against bacteria and viruses in the water.