• Home
  • /Disinfect Wells and Tanks

How to disinfect wells, tanks, and large water barrels

Looking for information on how to disinfect wells and tanks? The following should be used as a guideline only. Always refer to the manufacturers directions first or contact us if you have any questions.

Always use clean containers which are designed for food or water storage

Chlorine tablets

Follow the manufacturers’ directions.

Iodine drops

Whenever possible use warm water (20°C or 68°F) and let the water stand for a minimum of 20 minutes after mixing and before drinking. For cold water (5 – 15°C) increase the waiting after mixing to 40 minutes. If you are using 2% tincture of iodine, use 10 drops (0.5 mL) for every one litre of water

Iodine tablets

Follow the manufacturers’ directions.

IMPORTANT NOTE: Pregnant women should not use iodine drops as it may have an effect on the fetus.

Using bleach to to disinfect water in tanks

You can use regular household bleach (approximately 5% chlorine) or commercial bleach products (approximately 10% chlorine).

The table below shows how much regular 5% bleach to add to various size water containers to disinfect relatively clean water. If your water source is suspect in any way, have it tested by a government approved lab before consuming.

If you are treating water from a lake, stream or shallow well, use twice as much of 5% household bleach as indicated in the chart below and wait twice as long before drinking, as it is more likely to contain chlorine-resistant parasites from animal droppings.

Let the water stand for at least an hour after adding the bleach before you start drinking it. If the water is colder than 10°C or has a pH higher than 8, let the water stand for at least two hours before drinking.

Gallons (liters) of water to be disinfected Amount of Household bleach (5%) to add*
1 gal (4.5 L) 2 drops (0.18 mL)
2.5 gal (10 L) 5 drops (0.4 mL)
5 gal (23 L) 11 drops (0.9 mL)
10 gal (45 L) 22 drops (1.8 mL)
22 gal (100 L) 3/4 tsp (4 mL)
45 gal (205 L) 1-1/2 tsp (8 mL)
50 gal (230 L) 1-3/4 tsp (9 mL)
100 gal (450 L) 3-1/2 tsp (18 mL)
220 gal (1000 L) 8 tsp (40 mL)
500 gal (2200 L) 6 tbsp (90 mL)
1000 gal (4550 L) 6.5 ounces or 12 tbsp (180mL)
Adding household bleach in these amounts will produce water with approx. 2 parts per million of chlorine (0.0002%)

Disinfecting Wells

The following methods are recommended for the disinfection of wells and springs that have been flooded or accidentally polluted.

Disinfection should be done only after the flood waters have receded.

In the meantime, boil the water thoroughly before drinking.

How to disinfect well water

Treat water with any of the 5% household bleaching solutions obtainable from a grocery store.

Pour into the well a quantity of the bleaching solution as indicated in the table below, start the pump and open all taps. If it is a dug well without a pump, the chlorine solution should be allowed to mix thoroughly in the well and then let stand for at least 24 hours.

When a chlorine odour is detected at the taps, close each tap and stop the pump.

Open the valve or plug at the top of the pressure tank, just before the pump is stopped, to allow the chlorine solution to come into contact with the entire inside surface of the tank. This valve or plug should then be closed.

Whether is is a dug well or one equipped with a pump, the chlorinated water should remain in the system for 24 hours.

Table of quantities of 5% household bleach required for disinfection of wells

Diameter of well, spring or pipe Amount of household bleach (5%) required for each 10 foot depth of water
2″ 1 tsp (5 mL)
4″ 4 tsp (20 mL)
6″ 10 tsp (50 mL)
8″ 7 tbsp (105 mL)
10″ 10 tbsp (150 mL)
12″ 13 tbsp (195 mL)
24″ 3.5 cups (875 mL)
36″ 2 qts (2.2 L)
48″ 3 qts (3.3 L)
60″ 5 qts (5.5 L)
72″ 7 qts (7.7 L)
96″ 3 gallons (13.5 L)
*Excess use of the recommended bleach may poison your septic field. A total and fecal coliform test should be repeated 7 to 14 days after a bleach treatment