Check cisterns for problems

Residents who have cisterns are being asked to check them.

Cistern water can be safe to consume, provided it is adequately treated and the cistern is maintained properly.

Department of Environmental Health officials ask say cisterns should be checked at least once a year for cracks and other defects in the walls and cover. House roofs and gutters also should be checked for defects and accumulated debris, states a press release.

Cistern covers should be made of durable, nonporous material, and should fit tightly to prevent insects and foreign matter from entering the cistern. A coping, or lip, should surround the cover to prevent contaminated runoff water from entering the cistern.

Downspouts and overflows should be fitted with screens, also to keep out debris and insects. A downspout diverter, which diverts water and allows it to go to waste, reduces the amount of debris and contamination that enters a cistern.

DEH officials also strongly recommend that the diverter be used during the first rains of the season, to allow the dirty water from the roof to go to waste. Once the first rains have cleaned the roof, homeowners can begin to catch the rain in their cisterns.

In addition to checks for defects, cisterns should be thoroughly cleaned at least once a year, or as often as needed, to minimise sedimentation on the bottom. Sediments are organic in nature and as a result, they reduce the effectiveness of disinfection chemicals and allow micro-organisms to grow.

The organic matter in the sediment reacts with chlorine to form toxic compounds and gases. Sedimentation can compromise the safety of cistern water; it should be kept to an absolute minimum.

People without experience in cleaning cisterns should not enter them. DEH officials emphasise that it is a confined space, and low oxygen and chemicals can make it dangerous.

They also urge residents to avoid cross-connecting cisterns with wells. Some householders use well water for their laundry or for flushing toilets, as an economical measure. However, if there are cross-connections between a contaminated well and your cistern or you are using the same piping for both sources, your drinking water supply can become contaminated and may cause you to become ill.

Also, disinfect all potable water (such as water used for drinking, cooking, bathing, etc.) before use. This can be done by heating water to a rolling boil for one minute or by treating the water with domestic chlorine bleach – two drops of bleach, for each gallon of water. Ensure that all containers handling cistern water are sanitised.

For more information about the safe collection and use of cistern water, contact DEH at 949-6696.


Cisterns should be disinfected after they are cleaned, after every heavy rainfall, every time you have it filled with water and at the minimum, every other week.

If the cistern is clean – with no residue on the bottom or sides – cisterns can be disinfected using fragrance-free domestic chlorine bleach, such as Purex or Clorox, at a rate of 3 fluid ounces (90 ml) to every 1,000 gallons of water.

If, after 30 minutes, there is no residual odour of bleach in the water, it means the chlorine has been used up and additional treatment is needed. Add half of the previous amount of bleach.

A residual bleach smell in the water is an indicator that the water has been satisfactorily disinfected. Check again, 15 minutes after the second treatment, to ensure there is a residual odour of bleach. If a little too much bleach has been added, agitation or allowing it to sit will allow the excess to dissipate naturally.

Always store bleach and other household chemicals out of direct sunlight, and out of the reach of children.

If you don’t know how much water your cistern holds, here’s how to calculate it. This will also help you to know how much bleach to use.

Volume of water (gallons) = length x width x depth x 7.5

Amount of bleach needed = volume of water in cistern x 2.5


.In an emergency, even if piped water supplies are not entirely cut off, they may be compromised. Please listen to all official advisories issued by the National Hurricane Committee or Hazard Management Cayman Islands, to know if you need to treat your tap water before use.

For more hurricane preparedness information, visit

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