Science 101: Is your tank water clean? How clean is your clean?

Thulani Shabangu is one of the founding members of the Vryheid Science Club. He has a BSc in Physics and Chemistry and hopes to instill his passion for science in the youth of Vryheid. If you have a question for the Science Club, send a whatsapp to 060 986 0731.

ONE goal of the municipalities is to provide safe drinking water to the community. In Vryheid, one of the areas where the effects of climate change struck the hardest, the reliance of the community on boreholes and plastic water tanks has increased. The municipal ‘clean water supply’ goal can be threatened by the increased dependence on boreholes and water tanks. This week, we will spare a boreholes’ issue and take a brief scientific look at the plastic water tanks.

Scientific fact 1:

When the sun strikes a material, it always interacts with it. The effects of this interaction depend mainly on the amount of radiation reaching the material, the chemical composition of the material and the period of exposure. This is also a case with plastic water tanks which are widely used in Vryheid.

Chemical composition of the tanks & toxicity

Most common plastic tanks in Vryheid are made of polyethylene. When temperatures are too high plastic (polyethylene) may leach and contaminate the water inside. In high quality tanks, this is prevented by a smooth lining inside the tank. The tanks must be coated and made UV resistant. However not all tank making companies are good at making the best possible UV resistant coating in these tanks which may pose a health risk to users. It is important to choose high quality tanks to avoid or minimise this factor.

How clean is your clean?

No matter how clean your water looks, it is not clean until a chemical test says so. There are many good and bad microorganisms that can only be seen using a microscope. The bad microorganisms are the harmful ones which may cause diseases. An ideal chlorination kills the bad microorganisms leaving your drinking water clean. Some of the bad microorganisms rely on sunlight and poor hygiene to survive and grow.


Different insects like mosquitoes may breed inside a poorly closed and seldom cleaned water tank. They may bring illness causing bacteria into the water. It is very important to use a well closeable tank which does not allow sunlight or insects to get in. The insects may get inside, find a breeding habitat and breed inside the water tank which may pose health risks especially if the water is used for drinking.

Cyanobacteria (Blue-Green Algae)

This is one class of algae that is mostly found in fresh water and sea water. It grows in conditions with sufficient sunlight and nutrients (NPK) in water. When cyanobacteria decompose, they decrease the oxygen levels in water. This kills other microorganisms in water that are oxygen dependent which intoxicate the water. The toxins caused by cynobacteria are called cynotoxins. The ingestion of different cynotoxins to a human being have different effects .There is a group of cynotoxins that attack the nervous system, the group that cause skin and liver related illnesses.

Halogenation (Chlorination) or bleaching of water hinders the growth of cyanobacteria but it must only be done by trained professionals since the excess of chlorine in water may pose health risks. Mixing rainwater with chlorinated water may intoxicate the water and allow room for cyanobacteria growth.


The use of water tanks mean reliance on stagnant water which may be a good environment for breeding and growing of some insects and microorganisms especially if the water is unchlorinated. The availability of such organisms in your water may sometimes pose a health risk. Some of the insects and microorganisms excrete poisonous substances, they die in water which may poison the water for drinking. Various oxygen independent bacteria are highly found in stagnant water.

Different types of mosquitoes may cause different diseases. The mosquitoes that transmit malaria and dengue fever breed in stagnant water. Dengue causing mosquitoes are mainly found on artificial water storage containers. Self-education about the proper management water tanks is important.


* Make sure you use a high quality plastic tank.

* Choose a darker tank in color.

* Block sunlight and make sure it doesn’t get inside. You may also cover the tank or put it in a darker place.

* Clean your tank frequently, preferably weekly.

* Regularly look into the tank. If the water, roof, walls or floor are dirty the tank must be cleaned.

* Check and repair leaks.

* Keep the lid on the water tank.

Issued by Thulani Shabangu

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