Disinfection
 

 

Recommended Procedure for Disinfection
of Small Quantities of Drinking Water


Many occasions arise which require the disinfection of small quantities of drinking water. Disinfection may be necessary because of temporary contamination of a supply which is satisfactory under normal conditions. It may be necessary to disinfect water that is contaminated during transportation.

Boiling is a very effective means of disinfection drinking water, but the process is bothersome and not often used. Chemical disinfection of small quantities of water for human consumption is much more popular, and if carefully accomplished is as effective as boiling.

Four items must be considered if chemical disinfection is to be effective: (1) the water must be free of turbidity or dirt, (2) the chemical must be applied in a sufficient amount to guarantee disinfection and must be uniformly distributed to contact every particle of water, (3) at least 30 minutes of contact time must be provided between the chemical and water to allow time for the chemical to destroy any disease causing bacteria or viruses, and (4) the water after treatment must be protected from further contamination.

The most widely used chemical for water disinfection is chlorine. This chemical is used by most municipal water systems and effectively destroys disease causing bacteria and viruses when applied in dosages far below the amount harmful to humans. The chemical can be purchased in the form of chorine gas, chlorine powder, or liquid chlorine. Household bleaches such as Clorox and Hilex are liquid chlorine. This form is best for treatment of small quantities of water because no equipment is required and the liquid can be easily measured by a dropper, spoon, or measuring cup.

Typically household bleaches will be 5.25% available chlorine., although it is possible to have slightly different solution strengths depending on the particular product. The first step in disinfecting drinking water is to determine the % available chlorine in the solution that can be obtained from grocery stores.

The next step is to determine the amount of chlorine to use in properly treating a quantity of water. The following table gives the amount of chlorine necessary to treat given quantities of water. By knowing the amount of water to be treated, the amount of solution can be determined from the table.

 

 Strength of Solution

Brand Name

Amount of Solution for Disinfection of Drinking Water

1 gallon

2 gallons

3 gallons

4 gallons

5 gallons

5.25%

Clorox, Hilex, Purex

3 drops

6 drops

9 drops

12 drops

15 drops


The water to be treated should be place in a clean container. After the chlorine solution is introduced into the water, it should be agitated slightly to mix the chlorine and water. The container should then be covered and the water allowed to stand for at least 30 minutes before using. An odor and taste of chlorine should be apparent. These will disappear with time, are entirely harmless to humans, and are your guarantee of safe drinking water.

 

Recommended Procedure for Chlorine Disinfection of Water Wells
(Reference - AWWA A100-6, Standard for Deep Wells)

 

Introduction

A water well should be thoroughly cleaned and disinfected with a strong chlorine solution after:

  • Original Construction
  • Any Repair or Maintenance
  • Flooding
  • A Period of Non-useTwo or More "Unsafe" Bacteriological Water Samples that are Traced to the Well

Adequate chlorine requires a certain chlorine dosage for a minimum contact time - 100 parts per million for 2 hours, or 50 parts per million for 8 hours, or 25 parts per million for 24 hours.

Chlorine for disinfection for these water systems can be either 5.25% sodium hypochlorite solution or 65% calcium hypochlorite powder. A 5.25% hypochlorite solution is common house-hold bleach such "Hilex", "Clorox", or "Purex" available at grocery stores and supermarkets. The 65% calcium hypochlorite powder is available from chemical supply houses and is known commercially as "HTH", Perchloron", or "Pittchlor".

Recommended Procedures

1. Determine the chorine dosage for the desired contact time from the following table:

 

  AMOUNT OF CHLORINE NECESSARY PER 10 FEET OF WATER IN WELL

 

Inside diameter of well casing

5.25% Sodium Hypochorite (Bleach)

65% Calcium Hypochorite

100 ppm* for 2 hours

50 ppm* for 8 hours

25 ppm* for 24 hours

100 ppm* for 2 hours

50 ppm* for 8 hours

25 ppm* for 24 hours

1¼ inches

1/8 fl oz

- -

- -

- -

- -

- -

2 inches

1/2 fl oz

1/4 fl oz

1/8 fl oz

- -

- -

- -

3 inches

1fl oz

1/2 fl oz

1/4 fl oz

- -

- -

- -

4 inches

1½ fl oz

3/4 fl oz

3/8 fl oz

- -

- -

- -

6 inches

4 fl oz

2 fl oz

1 fl oz

1/4 oz

1/8 oz

1/16 oz

8 inches

7 fl oz

3½ fl oz

1 3/4 fl oz

1/2 oz

1/4 oz

1/8 oz

10 inches

10 fl oz

5 fl oz

2 fl oz

3/4 oz

3/8 oz

3/16 oz

12 inches

2 cups

1 cup

1/2 cup

1 oz

1/2 oz

1/4 oz

18 inches

4½ cups

2¼ cups

1 1/8 cups

2½ oz

1¼ oz

5/7 oz

24 inches

7½ cups

3 3/4 cups

1 7/8 cups

4½ oz

2¼ oz

1 1/8 oz

36 inches

17½ cups

8 3/4 cups

4 3/8 cups

10 oz

5 oz

2½ oz

* ppm = parts per million 1 heaping tablespoon of 65% chlorine powder = 1/2 oz. 8 fluid ounces = 1 cup

 

2. Prepare a chlorine solution, lift well pump, and pour the chlorine solution into the well.

3. Lower the pump and operate until a chlorine odor is noticed at all discharge points.

4. Leave the chorine solution in the unit for the recommended contact time. Do not use the water.

5. At the end of the contact time, pump the well to waste until the chlorine odor cannot be detected.
DO NOT ALLOW THE WATER TO ENTER A RIVER, LAKE, OR STREAM.

6. Pump the well for considerable period of time and collect a bacteriological water sample and submit it for testing.

 

Recommended Procedure for Chlorine Disinfection of Spring Box,
Elevated Storage, Ground Reservoir, Cistern, Water Treatment Plant Basin

 

Introduction

A ground reservoir, elevated tank, spring box, cistern, or water treatment plant basin should be thoroughly cleaned and then disinfected with a strong chlorine solution after:

  • Original Construction
  • Any Repair or Maintenance
  • Flooding
  • A Period of Non-useTwo or More "Unsafe" Bacteriological Water Samples that are Traced to the Well

Adequate chlorine requires a certain chlorine dosage for a minimum contact time - 100 parts per million for 2 hours, or 50 parts per million for 8 hours, or 25 parts per million for 24 hours.

Chlorine for disinfection for these water systems can be either 5.25% sodium hypochlorite solution or 65% calcium hypochlorite powder. A 5.25% hypochlorite solution is common house-hold bleach such "Hilex", "Clorox", or "Purex" available at grocery stores and supermarkets. The 65% calcium hypochlorite powder is available from chemical supply houses and is known commercially as "HTH", Perchloron", or "Pittchlor".

Recommended Procedures

1. The unit to be disinfected should be full of water.


2. Determine recommended chlorine disinfection dosage for the desired contact time from the following table:

 

  AMOUNT OF CHLORINE NECESSARY FOR DOSAGE AND TIME COMBINATIONS

 

Volume of Box, Basin, Reservoir or Cistern

5.25% Sodium Hypochorite (Bleach)

65% Calcium Hypochorite

100 ppm* for 2 hours

50 ppm* for 8 hours

25 ppm* for 24 hours

100 ppm* for 2 hours

50 ppm* for 8 hours

25 ppm* for 24 hours

50 gal

1½ cups

3/4 cup

3/8 cup

- -

- -

- -

100 gal

3 cups

1½ cups

3/4 cup

- -

- -

- -

200 gal

6 cups

3 cups

1½ cups

- -

- -

- -

500 gal

1 gal

7½ cups

3 3/4 cups

9½ oz

- -

- -

1,000 gal

2 gals

1 gal

7½ cups

1 lb 3 oz

9½ oz

- -

2,000 gal

4 gals

2 gals

1 gal

2 lb 6 oz

1 lb 3 oz

9½ oz

5,000 gal

- -

5 gals

2½ gals

6 lbs

3 lbs

1 lb 8 oz

10,000 gal

- -

- -

5 gals

12 lbs

6 lbs

3 lbs

20,000 gal

- -

- -

- -

24 lbs

12 lbs

6 lbs

50,000 gal

- -

- -

- -

60 lbs

30 lbs

15 lbs

100,000 gal

- -

- -

- -

120 lbs

60 lbs

30 lbs

* ppm = parts per million

3. Completely mix the chorine dosage throughout the unit to be disinfected.


4. Leave the chorine solution in the unit for the recommended contact time.


5. Do not use the heavily chlorinated water.


6. At the end of the contact time, remove the water from the unit and discharge to waste.

DO NOT ALLOW THE WATER TO ENTER A RIVER, LAKE, OR STREAM.


7. Fill the unit with clean water and collect a water sample for bacteriological testing after one or two days of use.

.