Chlorine is an effective and low-cost chemical for disinfecting water storage tanks. We are often asked, how much chlorine is needed to treat water? How much chlorine bleach do I put in my water tank? Using the charts below you can find out how much Chlorine Bleach is needed to disinfect and purify specific quantities of water, for example, 1,000 gallons. On this page we will talk more about the chlorine to water ratio and how much chlorine to put in drinking water. If your tank is new, has been worked on recently, or you know it is contaminated, perform a “shock chlorination” with 50 to 100 parts per million (PPM) and let sit for 12 to 24 hours.

1. How Much Chlorine Bleach To Add to Kill Bacteria in My
Storage Tank or Cistern?
Storage tanks can become contaminated by:
• Natural disasters (floods, earthquakes,
wildfires)
• Contaminated groundwater
• Poorly fitting lids or tops
• New well construction
• Well recently serviced
• Filled with contaminated trucked-in water
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2. Above ground storage tanks
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3. Below ground storage tanks (cisterns)
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4. Types of common chlorine bleach available
Laundry bleach 5%
Sodium hypochlorite
Pool chlorine 10 to 12.5%
Sodium hypochlorite
Powdered bleach 65%
Calcium hypochlorite
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5. Two Methods:
Drain tank entirely, wash down or clean inside if
possible and refill.
OR
Add chlorine to existing tank full of water.
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6. Decide on Chlorine Levels
“Shock Chlorinate” by adding a high level of chlorine 50 PPM
and disposing of water on ground or allowing to sit until
chlorine dissipates.
OR
“Maintenance Disinfection” by adding 5 to 10 PPM.
If chlorine levels drop to 1 PPM or under, you may be able to
use the water in the home.
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7. Disinfection of a contaminated tank - 50 PPM
1. Drain tank. Clean or wash down interior walls of tank first if
possible.
2. Be careful of confined spaces – don’t climb into an enclosed
space. Never mix chlorine with other chemicals.
3. Fill tank ¼ full of potable water
4. Mix chlorine with 5 – 10 gallons of water and pour into tank
5. Fill tank and let sit for 12 hours
6. Run water in home until you smell chlorine or use a test kit.
7. Drain and pump water with the 50 PPM chlorine residual to
lawn or ground. Do not run into septic tank or let flow to
creeks or waterways.
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8. Adding low level of chlorine to full tanks - 10 PPM
1. Mix chlorine with 5 – 10 gallons of water and pour into
tank
2. If possible, connect garden hose to outside pump and
allow water to circulate for 1 – 2 hours to make sure
chlorine is distributed throughout tank.
3. Run water in home until you smell chlorine or use a test
kit.
4. Avoid having a high level of chlorine in household water if
you are on septic tank.
5. Drain and pump water with the 10 PPM chlorine residual
to lawn or ground. Do not run into septic tank or let flow
to creeks or waterways.
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9. How much chlorine bleach to add to storage tank?
Residual: 50 mg/L (PPM) 10 mg/L (PPM)
Tank Size Bleach 5.25%
Bleach 10% -
12.5%
Chlorine
Granules
Bleach 5.25%
Bleach 10% -
12.5%
Chlorine
Granules
50 1 cup ½ cup 1 oz 1.6 oz 1 oz ½ teaspoon
100 2 cup ¾ cup 2 oz ½ cup ¼ cup 1 teaspoon
250 5 cup 2.5 cups 5 oz ¾ cup 1/3 cups 1 ¼ tablespoons
500 10 cup 5 cups ¾ cups 2 cup 1 cups 2 ½ tablespoons
1000 1 gallon ½ gallon 1 ½ cups 3 ½ cups 1 ½ cups 5 tablespoons
2500 2 ½ gallons 1 gallon 3 cups ½ gallon 1 quart 1/3 cups
5000 5 gallons 2 gallons 6 cups 1 gallon ½ gallon ¾ cups
10,000 10 gallons 4 gallons 12 cups 2 gallons 1 gallon 1 ½ cups
Chlorine volumes are approximate and have been rounded to an even measurement quantity.
Laundry bleach (Clorox etc) = 5.25% Pool bleach = 10% to 12.5% Powdered chlorine = 65%
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10. Questions? Call us at 888-600-5426 or email us at
support@cleanwaterstore.com