Active Chlorine

Chlorine’s effectiveness

Chlorine eliminates 99% of bacteria and protects water against recontamination * when residual chlorine is left in the water.

Chlorine is by far the most commonly-used disinfectant in the world, states the World Chlorine Council. Where widely adopted, chlorine has helped to virtually eliminate water-borne diseases such as cholera, typhoid and dysentery. Chlorine also eliminates slime bacteria, moulds and algae that commonly grow on the walls of water pipes and water storage tanks.

It should be understood that even if bacteriological contamination of water is responsible for the great majority of waterborne diseases, active chlorine (as well as active chlorine produced by WATA® devices) only treats bacteriological contamination of water. Active chlorine does not take away the different sediments and materials that make the water troubled. Active chlorine does also not treat chemical contaminations of water (e.g. by heavy metals, arsenic, fluorine,…).

* (OMS, 2004, Water treatment and pathogen control, IWA publishing, p 44-50)

The WATA ® device produces a chlorinated compound, sodium hypochlorite

Today, sodium hypochlorite is produced in 85 countries. Production has risen from 35,000 tons at the end of the 19th century to 44 million tons today. It is still used in most water supply networks in northern Europe and North America to guarantee the perfect hygiene of drinking water.

While some of the other chlorinated compounds used for water treatment are dangerous, the sodium hypochlorite produced by WATA® is less corrosive. Ingestion of sodium hypochlorite is unpleasant but not dangerous. The chlorine solution produced with WATA®:

  1. Has a four times lower concentration of chlorine than bleach.
  2. Has a lower pH than bleach, therefore it is more active and more efficient as a disinfecting agent.

For use in bottles, we recommend the stabilisation of chlorine by adding caustic soda.

Conservation & stabilization of a sodium hypochlorite

Proper storage is needed to guarantee its stability over time.

The active chlorine concentrate must be stored in opaque, non-metallic and properly closedreceptacle. Store the receptacle in a cool room, away from the light. A high storage temperature reduces the stability of the solution, thereby causing a decrease of the concentration and an accelerated decomposition of the active chlorine into chlorates. Note that a full receptacle will keep longer than a half-empty one, where the air will oxidize the concentrate.

To ensure a greater longevity of the sodium hypochlorite solution, the presence of metallic impurities in the raw materials used for the production (water and salt) need to be avoided.

Storage life of the solution produced by WATA®.

The active chlorine concentration of the sodium hypochlorite produced by WATA® is not stable over time. Antenna recommends to use the solution within 24 hours following the production.

If you would like to use your chorine solution for a longer period of time, it is necessary to stabilize the solution following the method described in the following document.

Stabilizing a solution of sodium hypochlorite 

The pH of the sodium hypochlorite solution needs to be increased to a value between 11.8 and 12 by adding a solution of caustic soda 5M. This operating process requires the use of a pH-meter or of pH-indicator strips. It also requires laboratory skills but ensures a good-quality product with a shelf life of at least 6 months. Current legislation in the country where you are operating must be respected. The legislation in force in your country has to be respected. A quality control procedure validated by the local authorities must be set up.

Operating method for using caustic soda to stabilise sodium hypochlorite

Control of the active chlorine concentration of stabilized sodium hypochlorite

Once stabilized, the concentration of the solution of sodium hypochlorite cannot be directly measured using the WataTest® reagent. For the WataTest® to be used on a stabilized solution, the sample to be tested has to be acidified using citric acid, following the operating mode presented in this document: (en cours de rédaction). An alternative method, proposed by Antenna, to measure the active chlorine concentration consists of titrating the sample with sodium thiosulfate, following the instructions presented in this document.

When distributing chlorine flasks at a large scale, it is required, for each production, to control the concentration of the stabilized solution of sodium hypochlorite using the thiosulfate titration method, which offers a better accuracy of the measurement.

For more information on the studies led by Antenna on the stabilization of the sodium hypochlorite, visit the “Research and development” page.