How To Keep Water Fresh In A Storage Tank

One of the easiest ways to save a little money around your home or homestead is using water storage tanks that can be rigged to capture rainwater from roofs via the guttering. This might not only save you cash, but you might be reliant on boreholes or streams for water and have no other option.

Filling and emptying the tank is relatively easy, but what about the time that the water spends in the tank? Is the water perfectly safe to drink, and for how long? How do you keep water fresh in your storage tank?

Buy an opaque tank that allows no light in for algal growth. Place it out of direct sunlight if possible and prevent contaminants from entering the tank via screens and filters. Clean the tank physically each year or two, and add chlorine in measured quantities when the water is cloudy or smells.


Unless you start with the correct storage tank, your water supply may be compromised, and a galvanized metal tank or a polyethylene tank with a UV rating is a good place to begin. The higher you store the tank, the better the water pressure for showers, etc., but it will need to be very stable as water is heavy. A gallon weighs 8.3 lbs / 8 L weighs 8 kgs, and a 660 gal / 3000 L tank can do a lot of damage if it falls.

Algae in water do not grow well in colder regions but use photosynthesis to reproduce, so avoid any tanks that do not block out sunlight 100%. If your tank does not allow light in, algae cannot grow.

Since other forms of bacteria that affect water can thrive where temperatures are high, consider protecting the tank from direct sunlight if you’re in a warm to hot region. The initial choice of the tank’s location is the best time to do this.

Avoid storing water tanks near gasoline, kerosene, pesticides, or similar substances as they can penetrate the plastic.

If you are filling the tank from house gutters, place a filter near the inlet to catch and debris from the roof. A dust cover is also a good measure to keep storage tank water fresh, as it keeps out both dust and light.

Tip: Make sure you have an overflow pipe in place, allowing excess water to leave the tank from the top.

Combatting Most Disease-causing Micro-organisms

Sometimes it’s just impossible to keep all light from the water, and an algal growth begins, and there is no point in collecting rainwater if it is only going to be ruined by algae growth. To combat this and to purify tank water that smells strange or is giving you a different cause for concern, do the following:

  • Granular calcium hypochlorite. Make a chlorine/water solution that you will use to disinfect your tank’s water. As a safety precaution, do this in a well-ventilated area and always wear eye protection. Add one heaped teaspoon (approximately ¼ ounce) of HTH (high-test granular calcium hypochlorite) to 2 gals / 7.5 L of water, stirring until the particles have all dissolved.

This mixture produces a chlorine solution of roughly 500 milligrams per liter. To clean your tank’s water, add one part chlorine solution to 100 parts of the water you are treating. This is akin to adding 1 pint of the solution to 12.5 gallons of water.

The chlorine taste may be too strong, so pour the water from one clean container to another slowly,  and let it stand for one to four hours before using it. 

CAVEAT: HTH is very powerful, so we recommend you follow all instructions on the label for the safe handling and even storage of the chemical.

  • Household iodine. You may already have iodine in your medicine or first aid kit. Drop five drops of 2%-strength tincture of iodine to every quart (or liter) of water that you wish to disinfect. If the water starts cloudy or discolored, add twice as many drops. Stir the solution and let it stand for 30 – 60 minutes before using it.
  • Water purification tablets. You can purify water with tablets containing chlorine dioxide, chlorine, iodine, or certain other disinfecting agents. The tablets are available at pharmacies and sporting goods stores or online. Follow all instructions on the product labels as each product may have different strengths to the next.

Heavy Cleaning

Every few years, three or four in most cases, it might become necessary (or desirable) to give your tank a good scrubbing, both inside and out. Empty the tank as completely as possible using the outlet valve (or tap) near the bottom. You’re now faced with having to climb in, but attaching the brush you are planning to use to a long pole might make it possible to clean the tank without entering it.

Use a mixture of hot water and a medium-strength detergent ( laundry soap powder is fine) to scrub clean all the tank’s internal surfaces (including the ceiling). This can be achieved with a sturdy brush or a high-pressure water jet. Take special care when rinsing corners and joints so that none of the cleaning liquid remains. Even minute amounts of some liquids can give the water a bad taste.

Continue flushing the tank until there are no longer traces of detergent in the water before refilling the tank with clean water once again. Note that tanks in hot areas should be cleaned every couple of years, and we recommend cleaning the tank every year, just before the rainy season if possible.

Post-Treatment: Precautions

Avoid using the treated water for drinking until after the smell of chlorine has departed completely. This aeration may take a day or two, depending on the temperature, wind conditions, and ventilation. Clearance of the chlorine odor is quicker with the lid removed, but bird and rodent droppings are a secondary threat.

Boiling chlorinated water or using it for cooking will usually evaporate the chlorine, from where it will become tasteless and safe to drink. However, people sensitive or allergic to chlorine should avoid primary contact with the treated water until the smell has disappeared.

How Long Can Water be Safely Stored?

Indefinitely. Water itself does not go bad, but pathogens and micro-organisms enter the water and cause problems, much like fleas on a cute puppy. Is the puppy bad? Remove the ‘fleas’ in your water, and your water returns to its pure state. Sure, water can become so toxic that it does not return to its original state of purity, but this will not happen in your storage tank.


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