Disinfecting Drinking Water
To disinfect drinking water means to clean or sterilize it so that it does not infect humans and animals, and their surrounding environments. You disinfect water when there is a chance it carries germs that could make you sick.
When should I disinfect my drinking water?
In B.C., drinking water suppliers are required to treat raw water to remove germs that can make you sick. However, there may be times when you need to disinfect your own drinking water, such as when:
- Your community is given a ‘boil water’ notice.
- You get your drinking water directly from a stream, river, lake, or creek, or from a shallow or improperly constructed well.
- Tests of your water show it has human waste (feces) in it, which is called fecal coliform.
- A flood, earthquake, or other disaster has disrupted the water supply in your community.
- You are travelling in an area where water is not well treated.
- You have a weakened immune system.
Why should I disinfect my drinking water?
When you disinfect drinking water, you kill germs such as bacteria, viruses, and parasites. Many different diseases are spread by germs and can infect drinking water. These are called ‘water-borne infections’. Common infections include Campylobacter, Salmonella, Cholera, Amoebic dysentery, Giardia (beaver fever), Cryptosporidium, and Toxoplasma.
Water-borne infections happen when animal or human feces containing these germs get into drinking water.
Open waters such as lakes and streams are more likely to get infected than water flowing deep under the ground. The closer water is to the surface, the greater chance germs can get in the water.
What is the best way to disinfect water?
- The best way to kill germs such as bacteria, viruses, and parasites, is to boil the water.
- Boil water at a full boil for at least 1 minute. If you are using an automatic shut-off kettle, make sure the water has boiled for 1 minute. At elevations, over 2,000 meters (6,500 feet) boil water for at least 2 minutes to disinfect it.
- Let the water cool. Always store your clean water in clean containers made for storing food or water.
- Boiling does not make heavily polluted water safe.
Can I use bleach to disinfect water?
Yes. If you cannot boil water, you can disinfect it using unscented household bleach. Do not use scented bleaches, colour-safe bleaches, bleaches with added cleaners, or non-chlorine bleach.
Bleach will kill some, but not all the different types of germs that could be in the water. Water disinfected with bleach is called ‘treated water’. Bleach does not work if the water is heavily polluted or when polluted with chemicals. Boil the water if you are concerned your water has parasites such as Giardia or Cryptosporidium. If you are ever unsure about the safety of your water, even after it has been treated with bleach, do not consume it.
Bleach works best when added to warm water that is about 20˚C (68˚F). To treat your water, add 2 drops (0.1 mL) of unscented household bleach (about 5.25% chlorine) to 1 litre of warm water.
Mix the bleach and water together. Cover it and let it stand for at least 30 minutes before drinking. You should notice a slight chlorine smell after the 30 minutes. If you don’t, add another 2 drops. Let the water to stand for another 15 minutes.
If the water is cloudy, colder than 10˚C (50˚F), or if your water is from a lake, stream, or shallow well add 4 drops (0.2 mL) of unscented household bleach (about 5.25% chlorine) to 1 litre of water.
Mix the bleach and water together. Cover it and let it stand for 1 to 2 hours before drinking. If the treated water has a strong taste of chlorine, let the water stand open to the air for a few hours. You can also pour it back and forth from one clean container to another several times. The longer the treated water stands the better it works to disinfect the water.
If you are using chlorine tablets, follow the directions on the package.
What if the water is cloudy or murky?
If the water is cloudy or murky, filter it before boiling or treating the water.
Pour the water through a clean cloth or coffee filter. Let any remaining bits settle to the bottom. Pour off the clear water into clean containers made for storing food or water. The water might still look a little cloudy. If you are ever unsure about the safety of your water, even after it has been filtered, do not consume it.
Can I use iodine to disinfect water?
Yes. You can use iodine but only for over a short period of time. If you use iodine for more than 1 to 2 months, you could get thyroid problems. Pregnant women should not use iodine drops to disinfect water as it could harm the unborn baby.
Iodine works best when added to warm water that is about 20˚C (68˚F). To treat warm water, add 5 drops (0.25 mL) of 2% Tincture of Iodine to 1 litre of warm water.
Mix the iodine and water together. Let it stand for at least 30 minutes before drinking.
To treat cold water that is between 5 to 15˚C (41-59˚F), use the same amounts, but let it stand for 40 minutes before drinking.
If you are using iodine tablets, follow the directions on the package.
Can I use filtration or other treatment methods to disinfect water?
If your drinking water will require treatment for a long period of time, you may want to think of other sources of drinking water, such as bottled water, or installing a filtration system. If you are going to install an filtration system, make sure to check with a reliable supplier who can help you with installation and ongoing maintenance.
To remove some types of germs, such as Giardia, filters must have an absolute pore size of 1 micron or less, and be certified by the National Sanitation Foundation (NSF) International or another accredited third party agency. For more information on the National Sanitation Foundation, visit www.nsf.org.
Jug-type water filters (such as Brita®), are not made to remove germs from an unsafe water supply and will not remove Giardia. Some built-in water filtration systems will remove Giardia, but they need regular and thorough maintenance to work well. For information on certification of treatment devices, visit the Standards Council of Canada (SCC) at www.scc.ca.
Other types of water treatment units, such as distillation and UV units are also available. Check with local water purification suppliers or your local environmental health officer for more information. The treatment unit should be certified by NSF International, or another accredited third party agency for cyst reduction or inactivation.
When should I use disinfected water?
Use treated, boiled (and then cooled water), or store-bought bottled water for the following activities:
- Making baby formula.
- Brushing your teeth.
- Making coffee or tea.
- Cleaning raw vegetables and fruit.
- Making drink mixes such as using juice concentrates or drink crystals.
- Washing dishes. If you wash dishes by hand, let them air dry. If your dishwasher does not have a hot or sanitation cycle, soak the dishes for 1 minute in a solution of bleach and warm water. Mix 2 ml of bleach for every 1 Litre of untreated water.
- Filling pet dishes.
- Making ice cubes. Freezing does not kill germs or clean the water.
- Bathing children.
To reduce the chance of your child swallowing water that might still have germs, give sponge baths using clean water. Adults can bathe or shower using water that has not been disinfected, as long as they do not swallow any of the water. After bathing or showering, wash your hands with disinfected water.
For More Information
If you have any questions about your drinking water, contact your local environmental health officer or your local health authority.
For more information, see the following HealthLinkBC Files:
- HealthLinkBC File #05b Should I Get My Well Water Tested?
- HealthLinkBC File #56 Preventing Water-Borne Infections For People with Weakened Immune Systems
- HealthLinkBC File #69b Formula Feeding Your Baby: Safely Preparing and Storing Formula