​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​What can cause my well water to be unsafe?

Your water might be contaminated (unsafe to use) with harmful bacteria or chemicals if:

• your water well has flooded
• surface water got into the wellhead (the part of the well you can see above ground) and down into the well casing (material that supports the sides of the well)

Wells in pits or basements can also flood or be contaminated. 

When flooding happens, you need to have your well checked by a licensed water-well contractor. Even if your well looks fine, bacteria and chemicals can still get in.

If my water well has flooded, can I use the water?

If your well has flooded, don’t use the water to drink, cook, or bathe. Use a different​ safe water source instead, such as municipal truck-fill, bottled water, or a neighbour’s well that isn’t flooded. If this isn’t possible, boil your water for 1 minute in a rolling boil to kill harmful bacteria before you use it. Learn more about boiling water to kill bacteria. If your well is contaminated with chemicals, boiling won’t help to make the water safe.

Don't use the water until a licensed water-well contractor has checked your well and the floodwater has been flushed or purged from the casing, shock chlorinated​, and tested.

What do I need to do to the well and pump?

Floodwaters can carry waste (such as wood, rocks, and metal) that can damage the well casing, electrical parts, and the pump.

When the floodwaters have gone down, call a licensed water-well contractor to check your well system. The pump (including valves and gears) might need to be cleaned to remove any soil or sand.

​ Don’t turn on the pump after a flood until a qualified electrician or a licensed water-well contractor checks the wiring system. You could damage the well and pump or even get electrocuted (harmed by electric shock).

Do I need to have my well and plumbing disinfected after flooding?


After flooding, your well and the whole plumbing system connected to it need to be shock chlorinated. This is a way to kill harmful bacteria.

Do I need to have my well water tested?

Before you use your well again after it has flooded, have the water tested for bacteria​. 


You can get sample bottles and testing instructions from an Alberta Health Services Environmental Public Health​ office. After testing, they will tell you if your water is safe to use. Learn more about drinking water bacteria test results.


If you think your well has been contaminated with chemicals, contact Environmental Public Health​ for testing.

How do I protect my well from flooding again?

When the flood is over and your well is safe again, check with a licensed water-well contractor or Environmental Public Health to learn how to protect your well from future floods. This may include:

• extending your well casing
• installing a flood-proof cap with an extended vent
• moving your well
• upgrading pit wells​​

​​​​​​​​​​​If you think your private well water is contaminated (unsafe to use) because of bacteria, contact your​ l​ocal public health inspector for advice. You can also try to shock chlorinate your well to kill harmful bacteria. The information below is about shock chlorination.

How do wells get contaminated with bacteria?

There are many reasons your well could become contaminated with bacteria.

Surface water and shallow groundwater have harmful bacteria in them, so some types of wells have a higher risk of getting contaminated, like:

• shallow wells
• wells that are connected to surface water
• wells surrounded by porous material (like sand or gravel)
• wells that were poorly constructed

Changes in the aquifer (the underground layer of rock that holds water) or changes to your well as it gets older can also put it at risk of getting contaminated.

Surface water that pools next to or over top of the wellhead (the part of the well you can see above ground) may also cause contamination.

Deep wells have less risk of contamination because the water source is more protected from harmful bacteria. But if E. coli or total coliforms are found in a groundwater well through a proper water sample, then the water is contaminated no matter how deep the well is.

​Before you shock chlorinate, you have to find out the reason your well is contaminated. That way you can fix the problem and stop it from happening again.

How does shock chlorination work?

Shock chlorination is a way to kill harmful bacteria and any bacteria you don’t want in your water (such as bacteria that reduce iron or sulphur). To shock chlorinate, you add a concentrated chlorine solution to the water in your well casing (material that supports the sides of the well). Some of this water will move outside your well and into the aquifer. Then you flush the chlorinated water through the system and let it sit for a certain amount of time.​ Download a step-by-step guide for shock chlorinating your well.

Does shock chlorination always work?

No. Shock chlorination doesn’t always work. The chlorine only disinfects (kills germs) in the water that it has had contact with for the right amount of time. If you don’t know or don’t fix the source of the problem, your well can become contaminated again.

Shock chlorination may not work in wells that have never been shock chlorinated or have not been regularly cleaned and maintained. Over time, bacteria can attach to the well casing and grow, forming a slimy layer called biofilm. ​Biofilm can make shock chlorination not work as well. You may need to hire a licensed well driller to find and scrub away the biofilm before you shock chlorinate your well.

What if shock chlorination doesn't work?

If water testing results show you still have bacteria in your well water after you shock chlorinate, you need to find out why. If you can’t find the reason or fix it, shock chlorinating again likely won’t help to make your water safe.

If shock chlorination doesn't work, you may need to think about:

• installing a water treatment system that can disinfect properly
• continuing to boil your water before you use it
• using another source of drinking water

You can also drill a new well (which is expensive) and properly plug the old well. But if the aquifer is the source of the problem, which is sometimes hard to know, your new well may also be contaminated.

When should I test the water after shock chlorination?

Test your water at least 7 days after the chlorine has been flushed from the well. If the sample has no bacteria, test your water again 14 to 30 days after shock chlorination. This is because you want to get a sample that shows the natural, untreated water from the aquifer.

It’s also a good idea to get another water test within 3 months or after snow melts (in the spring), whichever comes first. This is to make sure the shock chlorination and anything else you did to fix the problem worked.

If you couldn’t find the cause of the problem, your well water may still be unsafe.

When can I drink the water after shock chlorination?

You can drink the well water after you do all these things:

1. Shock chlorinate your well.
2. Flush the chlorinated water out of the system.
3. Test a new water sample at least 7 days after the chlorine has been flushed from the well and the results show no bacteria.

Where can I learn more about safe drinking water?

If you have any questions about your water, contact Alberta Health Services Environmental Public Health​.

​​​​​​​​​​​​​​​​​​If I can’t boil my water during a boil water advisory, how can I make the water safer to drink?

Boiling water for 1 minute is always the best way to disinfect (to kill germs in) your water during a boil water advisory, or when your water is unsafe to use. But if you can’t boil your water, like if the power is out during a storm, you can do one of the following:

• Use disinfectants like chlorine or iodine to kill most germs that may be in the drinking water. You have to treat for parasites before you disinfect with chlorine or iodine.
• Buy bottled water from a safe source.

Will chlorine and iodine make my​ water safer?

Chlorine and iodine work well to kill bacteria and viruses. However, these disinfectants will not kill parasit​​​es like Cryptosporidium. It can be hard to know if there’s a risk of parasites in your water, especially in an emergency.

If you can’t boil your water, the best way to make water safe is by treating it for parasites and using chlorine or iodine.

What treatment can make my water safe from parasites?

You have to treat for parasites before you disinfect with chlorine or iodine. Before you use chlorine or iodine to disinfect water, use one of these treatments to remove parasites:

• Filter: You can buy filters at water treatment suppliers or hardware stores. Buy a filter that is rated at 1 micron absolute or smaller with a cyst rating of NSF 53 or 58 certification. After you filter the water, disinfect it with chlorine or iodine.
• UV disinfection pen: You can buy UV disinfectant pens at camping supply stores. The water needs to be very clear (not cloudy) for the UV treatment to work. Before you treat it, let the water sit in a container until any particles (sediment) settle. UV disinfection pens aren’t usually certified by a recognized agency, so you have to follow the exact instructions from the manufacturer. After the UV treatment, disinfect the water with chlorine or iodine.

How do I disinfect drinking water with chlorine?

You can use water purification tablets or bleach to disinfect your water with chlorine (also called chlorinateing your water).

Water purification tablets

You can buy the tablets from most outdoor supply or camping stores. Follow the directions on the package.

Bleach

To chlorinate your water using bleach, you will need:

• a 1-litre container
• a medicine dropper
• unscented household bleach (5.25% sodium hypochlorite)

If your water is clear:

1. Add 2 drops of bleach to 1 L of water.
2. Mix the water very well and let it stand for 30 minutes. If there is a slight chlorine smell and the water looks clear, it’s safe to drink.

If your water is cloudy:

1. Add 4 drops of bleach to 1 L of water.
2. Mix the water very well and let it stand for 30 minutes. If there is no chlorine smell, add 4 more drops of bleach and let the water stand for another 30 minutes. If there is a slight chlorine smell and the water looks clear, it’s safe to drink.

How do I disinfect drinking water with iodine?

Do not use iodine for more than 3 weeks each summer (in controlled doses, following the instructions below) because there is a risk of thyroid problems and iodine sensitivity.

Do not drink water disinfected with iodine if you:

• are pregnant
• have a thyroid problem
• are very sensitive to iodine

To disinfect water with iodine, you need liquid iodine (2%) or iodine tablets. You can buy iodine at most drugstores and some outdoor supply or camping stores. If you use tablets, follow the directions on the package. If you use liquid iodine, follow the directions below.

Liquid iodine works best when you add it to warm water at a temperature of 20˚C (68˚F).

• To disinfect clear, warm water (above 15˚C or 59˚F), add 5 drops (0.25 mL) of iodine to 1 L of water. Mix the iodine and water together. Let it stand for at least 30 minutes before drinking.
• To disinfect clear, cold water at a temperature between 5 to 15˚C (41 to 59˚F), use the same amounts as for warm water (5 drops of iodine to 1 L of water), but let it stand for 40 minutes before drinking.
• If the water is cloudy, add 10 drops (0.5 mL) of iodine to 1 L of water and let it stand for the times listed above, depending on whether the water is warm or cold.

If you have any questions about your water, contact Alberta Health Services Environmental Public Health​