How to Make a 0.5% Chlorine Solution

A chlorine solution can be made from:

Liquid household bleach. (Sodium hypochlorite)
Bleach powder. Chlorine compounds available in powder form (calcium hypochlorite or chlorinated lime)
Chlorine-releasing tablets. (Sodium dichloroisocyanurate)

Because of their low cost and wide availability, chlorine solutions prepared from liquid or powdered bleach are recommended.

Determine the amount of "active" chlorine:

Chlorine-containing compounds are described as having a certain percentage of "active" (or available) chlorine. It is the active chlorine in these products that kills microorganisms. The amount of active chlorine is usually described as a percentage, and differs from one product to another. This is important so that a chlorine solution with 0.5% "active" chlorine can be prepared.

Note: In countries where French products are available, the amount of active chlorine is usually expressed in "degrees chlorum." One degree chlorum is equivalent to 0.3% active chlorine.

1. Using liquid household bleach

Chlorine in bleach comes in different concentrations. You can use any concentration to make a 0.5% chlorine solution by using the following formula:

[% chlorine in liquid bleach divided by 0.5%] minus 1 = parts of water for each part bleach*

* Note that "parts" can be used for any unit of measure (e.g., ounce, liter, or gallon) and need not even represent a defined unit of measure (e.g., pitcher or container).

Example: To make a 0.5% chlorine solution from a 3.5% chlorine concentrate, you must use 1 part chlorine and 6 parts water:

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[3.5% divided by 0.5%] minus 1 = [7] minus 1 = 6 parts water for each part chlorine

2. Using bleach powder

Note that when bleach powder is used, the resulting chlorine solution is likely to be cloudy (milky). If using bleach powder, calculate the ratio of bleach to water using the following formula:

[ % chlorine desired divided by % chlorine in bleach powder] times 1000 = Grams of powder for each liter of water

Example: To make a 0.5% chlorine solution from calcium hypochlorite powder containing 35% available chlorine:

[0.5% divided by 35%] times 1000 = [0.0143] times 1000 = 14.3

Therefore, you must dissolve 14.3 grams of calcium hypochlorite powder in 1 liter of water in order to get a 0.5% chlorine solution.

3. Using chlorine-releasing tablets

Follow the manufacturer's instructions, since the percentage of active chlorine in these products varies. If the instructions are not available with the tablets from your supply source, ask for the product's instruction sheet or contact the manufacturer.