How Much Chlorine To Add to Storage Tank To Kill Bacteria

  1. Clean the storage tank or reservoir. Remove debris and scrub or hose off any dirt or other deposits or interior surfaces. Pump to remove any suspended solids or foreign matter in the water if possible.
  2. Scrub interior surfaces of storage or reservoir if applicable with a strong chlorine solution containing ½ gallon household bleach, or ¼ gallon of pool chlorine to each 5 gallons of water.
  3. Inspect the storage tank for cracks, leaks around the lid or man-way, or vents. Make sure no insects, rodents or other debris can enter the tank during normal operation of the tank and water system, by making sure the lid is tight fitting, and any vents are properly screened.
  4. Use the chart below (Table 3) to add enough chlorine bleach in the tank, to bring up the chlorine residual in the tank to the desired level. If you are using tank and need to continue to use the water in the tank after chlorination, consider adding enough chlorine to bring the levels up to 5 or 10 ppm and let sit for 12 hours or more.
  5. Table 3: Storage tanks: Disinfecting with liquid household bleach (5% Sodium Hypochlorite)
    If using pool chlorine(12% sodium hypochlorite) use half the amounts below.
    Storage Tank Gallons Approx. parts per million of chlorine residual achieved by adding 5% chlorine bleach, in the amounts below.
    1 PPM 5 PPM 50 PPM 100 PPM 200 PPM
    10,000 10 oz. 1.5 gallons 10 gallons 20 gallons 40 gallons
    5,000 5 oz. 3 qts. 5 gallons 10 gallons 20 gallons
    2,500 2.5 oz 1.5 qt. 2.5 gallons 5 gallons 10 gallons
    1500 1.5 oz 1 qt. 1.5 gallons 3 gallons 6 gallons
    1000 1 oz. 12 oz. 1 gallons 2 gallons 4 gallons
    500 1 Tablespoon 6 oz 1/2 gallon 1 gallon 2 gallons
    250 1.5 – 2 teaspoons 3 oz 1 qt. 1/2 gallon 1 gallon
    100 1 teaspoons 1.5 Tablespoons 1 pint or 2 cups 1 qt. 1/2 gallon

  6. If a thorough disinfection is needed and time is short, use a 50 ppm or 100 ppm residual and let sit for 2 to 6 hours. Drain and flush tank if using these higher levels of chlorine. Don’t put large amounts of chlorine residual into drains leading to septic tanks, and avoid discharge into creeks, rivers or lakes.
  7. Be careful if you have a steel storage tank, as corrosion may have occurred over time, and once the tank is cleaned it may develop leaks.
  8. Storage tanks: disinfecting with dry 1 gram chlorine pellets

    1 cup pellets = 200 pellets = 1/2 lb 2 cups pellets = 400 pellets = 1 lb
    25 pellets in 100 gallons = 50ppm 50 pellets in 100 gallons = 100ppm

    Storage Tank Gallons Approx. parts per million of chlorine residual achieved by adding dry chlorine pellets in the amounts below.
    1 PPM 5 PPM 50 PPM 100 PPM 200 PPM
    10,000 1 cup 2.5 cups 5 lbs 10 lbs 30 lbs
    5,000 1/2 cup 1.3 cups 5 cups 5 lbs 15 lbs
    2500 30 pellets 2/3 cup 2.5 cups 5 cups 15 cups
    1500 18 pellets 1/4 cup 1.5 cups 3 cups 9 cups
    1000 12 pellets 32 pellets 1 cup 2 cups 6 cups
    500 6 pellets 16 pellets 1/2 cup 1 cup 3 cups
    250 3 pellets 8 pellets 1/4 cup 1/2 cup 1.2 cups
    100 1 pellets 3 pellets 25 pellets 1/4 cup 1/2 cup
    Useful Measurements:
    1 cup = 8 fluid oz. 1 pint = 16 fluid oz.
    1 quart = 32 fluid oz. 1 gallon = 128 fluid oz.
    1 teaspoon = 1/6 fluid oz. 3 teaspoons = 1 tablespoon
    1 fluid oz. = 29.6 milliliter (ml) 20 drops = 1 ml.


  • Clean Water Systems & Stores, Inc., Water Treatment Equipment,Service & Supplies, Santa Cruz, CA