Emergency chlorination of farm water

Page last updated: Wednesday, 6 February 2019 - 9:11am

Chlorination effectively reduces problems with water colour, taste and odour, and treats bacterial contamination. Preventing contamination should be the first priority, and chlorination is for when prevention of contamination has failed and results in the water being unpalatable or a health risk to livestock or humans.

We recommend batch chlorination for contaminated water drawn from a dam or soak, and only recommend chlorinating dams under exceptional circumstances.

When to use chlorination

We recommend chlorination when prevention of contamination has failed, and contamination results in the water being unpalatable or a health risk to livestock or humans. We also recommend that chlorination is done by batch processing into tanks, after organic material and sediment has been removed, and cloudy or coloured water has been treated.

Contamination that may need chlorination

Water in dams, soaks, wells or tanks is likely to become polluted during periods of drought, near the end of summer or after summer storms.

Bore water is less likely to be polluted, unless the bore is near a shearing or milking shed, a piggery, a septic tank system or near some other source of pollution in the groundwater.

Rainwater tanks can become polluted from bird droppings and other material being washed from roofs. See our rainwater tanks page for more information.

Whatever the water source, the cause of the pollution must first be removed: for instance, carcases or rotting algae should be removed and burnt or buried.

Livestock water supplies

To prevent pollution, we recommend that livestock should not be allowed to drink directly from the source of water supplies (dams, soaks, creeks, ponds or lakes). To prevent livestock defecating or urinating in the water, or stirring up pollutants in the sediment of dams and soaks:

  • fence dams and soaks
  • cover wells and tanks
  • pump or siphon livestock water to tanks or troughs.

Livestock losses from contaminated water in Western Australia are low, but livestock welfare, health and productivity are commonly reduced by contaminated water supplies and increased salinity levels.

We recommend that you regularly check and test farm water supplies for contaminants and salt levels. Refer animal health problems to a veterinarian.

Chlorination of water for livestock

Batch chlorinate in tanks or troughs because:

  • there is less organic matter present
  • there is less sediment and suspended clay
  • there is less chance of re-contamination
  • the volume of water to be treated is more easily calculated
  • mixing the chlorination chemical evenly is easier.

We do not recommend chlorination of contaminated dams and soaks because:

  • large amounts of organic matter reduce chlorination effectiveness
  • the clay lining and suspended clay reduce chlorination effectiveness
  • there is a high chance of re-contamination
  • estimating the volume of water in a dam is difficult
  • evenly mixing the chlorinating chemical into the dam is difficult
  • in heavily contaminated water, treatment would have to be repeated daily to be fully effective.

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Domestic supplies

For any health-related water tank concern, please view the Department of Health's Water tanks on your property web page or contact the Department of Health.

Batch chlorinate water drawn from a dam or soak for domestic use. Chlorination of domestic water not used for drinking is not strictly necessary, but it is reassuring.

Recently chlorinated water will almost certainly have an aftertaste. After standing and aeration, the taste from chlorine alone will diminish but the ‘antiseptic’ or ‘chemical’ taste from reaction with organic matter in the water may persist.

Alternative domestic treatments

Boiling water for drinking is possibly an easier means of purification. Disinfecting tablets based on iodine are available from pharmacies. Filtration, reverse osmosis and ozone treatments are available for those prepared to invest capital for ease or peace of mind.

Chlorination procedures

For dams and soaks, the preferred system for chlorination is:

For tanks and troughs, chlorinate directly into the container.

Which chlorinating chemicals?

Use either granular calcium hypochlorite or liquid sodium hypochlorite. Do not use both at the same time. The Department of Health recommends that you do not use stabilised chlorine (cyanurate) for drinking water. Cyanurates are organic chlorination compounds intended for swimming pools, are more stable in sunlight when dissolved than the other chlorine compounds, but are more expensive and are not recommended for emergency chlorination of drinking water.

Calcium hypochlorite, or high test hypochlorite, contains about 70% available chlorine. It is in a granular form and more stable than bleaching powder and should be used within 2 months of the container being opened. Sodium hypochlorite is available as a number of bleach solutions containing 10–15% available chlorine: laundry bleach is usually 3–5%, and this solution is not stable and decomposes rapidly with age.

The chemicals required can be purchased from rural agencies, pharmacies and swimming pool agents.

How much chlorine?

All water has a ‘chlorine demand’, which is the amount of chlorine used in a given time by reaction with matter dissolved or suspended in the water. To disinfect contaminated water, chlorine added must be in excess of the chlorine demand, and allowed to remain in the water for sufficient time to disinfect the water supply.

Clear, clean water has a chlorine demand of about 10 milligrams per litre (the same as grams per 1000 litres); badly fouled water has a chlorine demand of about 100 milligrams per litre. These levels can be adjusted according to chemical analysis.

Once dissolved, chlorination compounds are decomposed rapidly by sunlight and heat, so water should be treated in the evening.

Table 1 Amounts of chemicals required to meet various chlorine demands per 1000 litres of water
Condition of water Chlorine demand (mg/L)

Calcium hypochlorite, 70%* (g)

Sodium hypochlorite, 10%* (mL)

Clean 1 1.4 10
Comparatively clean 10 14 100
Slightly fouled 20 29 200
Fouled 50 70 500
Badly fouled 100 143 1000

mg/L = milligrams per litre; g = grams; mL = millilitres
* percentage available chlorine

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Batch-wise chlorination management

Efficient chlorination can only be achieved by treating smaller volumes in containers, and preferably in covered tanks. Emergency containers, such as drums or troughs, could be used for smaller amounts.

You will find it easier to calculate the dose, and add and mix the chemical when treating smaller volumes of water.

Use a chlorine test kit, as used for swimming pools, to test the water.

Residual chlorine of at least 0.2mg/L after 2 hours contact indicates sufficient chlorination has occurred.

A smell of chlorine from the water on the morning after treatment indicates that sufficient chlorine has been present long enough to be effective. For certainty, use the chemical test.

Limitations to chlorination

Chlorination does not affect toxins causing botulism that are produced by organisms growing on putrefying carcases or rotting vegetable matter. The benefits of chlorination are not long-lasting and dosing must continue if contamination continues.

Through its germicidal effect, chlorine kills bacteria responsible for most forms of food poisoning, gastroenteritis, paratyphoid fever and dysentery.

Chlorination gives other benefits because it destroys some taste and odour-producing organisms, kills algae and slime organisms, and aids precipitation of iron. But some tastes are intensified and dead algae must be removed.

Water analysis

Contact the ChemCentre on +61 (0)8 9422 9800 or your local government's environmental health officer for advice.

Simple salinity tests can be obtained at most irrigation suppliers, rural agencies and your local DPIRD office.

Contact information

Tilwin Westrup
+61 (0)8 9780 6165