Science 101: Is rainwater safe for domestic use?

Thulani Shabangu is passionate about science and wishes to share his passion with the youth of AbaQulusi.

NATURAL science explains many natural phenomena, be it solar eclipses, origins of life, planetary motions, formation of stars etc. Our focus is on climate change which results in droughts and less rainfall. In this science column, I dedicated a whole month to talk about water quality.

In Vryheid, we’ve had a dry spell. Summer is coming. Even though rainfall levels are reduced, we can still expect little amounts of rainfall. People may collect rainwater and store it for use. We have looked at the quality of tank water and borehole water. This week we will focus on rainwater. Is rainwater safe for domestic use?

The journey of rainwater

From clouds to the ground and back to the clouds, the rainwater goes. This makes its journey interactive with a lot of pollutants which may pose a variety of health risks.

YOU MAY ALSO WANT TO READ: Science 101: Boreholes, more good water for drinking

AND: Science 101: Is your tank water clean? 

Air pollution

The air is not very clean and can pollute rainwater. In air, there is dust, chemical pollutants, bacteria, fungi and other pollutants. Air pollution varies with different areas. Urban and highly industrialised areas have higher chances of air pollution. Air pollutants may be soot, smog, dust and other toxic pollutants. Some pollutants dissolve in water in the atmosphere which may pollute rainwater.

Birds and insects

Birds and insects excrete on rooftops (catchment) and gutters. Insects may breed and sometimes die in gutters. The excreta of birds and insects sometimes carry pathogenic bacteria (bacteria that causes diseases). When insects die, some release poisonous substances which may contaminate the rainwater.

Chemical toxicity

The paint and the material that makes up the roof and gutter may intoxicate rainwater. The interaction of solar radiation with paint, the roofing material and gutters may lead to the leaching which may contaminate collected water. This may lead to a wide range of diseases caused by heavy metal toxins. Most people use the rooftop surfaces for catchment. The quality of the material used as a catchment must be high and non-harmful to humans. This is because it is in contact with the water that may be used for drinking.

Rainwater storage

How rainwater is stored also has effects on the quality of rainwater. Rainwater is stored mostly in tanks. We looked at the proper management and health risks associated with the use of plastic tanks last month.

Rainwater treatment

Bacteria produce endospores to survive unfavourable conditions like extreme temperature, pH and if no nutrients are available for growth. This is one reason why boiling is not a reliable treatment method for rainwater. Boiling water using a kettle is even worse since the water boils for a short period of time and the endospores can survive these temperatures. When the water cools down the endospores can germinate to form bacterial cells again. If the water is chemically intoxicated, boiling doesn’t detoxify the water.

Chlorination is recommended because it kills harmful microorganisms chemically. However it is important to do it under professional advice.


– Minimise the use of rainwater for drinking and cooking.

– Use rainwater for laundry and outdoor purposes like irrigation.

– Clean the gutters and the tanks frequently.

– If you use rooftop surfaces as your catchment, keep them clean.

– Have a clean and well-designed rainwater harvesting system.

– Keep the storage tanks sealed to block sunlight.

– The first flush of rainwater is normally the most contaminated.

– Make sure your catchment is not made of harmful materials to humans. This is because the material may leach and contaminate the water.

– Check for the physical (visible dirt) quality of water, colour and smell. The unusual colour and smell may be a sign of contamination in water. Visible particles of dirt must be filtered.

– If you use rainwater for drinking, chlorination is advised. This will only kill bad microorganisms in water but does not remove any toxic chemicals.

Written by Thulani Shabangu, Edited and Reviewed by Professor A Basson

Latest News


Next Story x
Nets destroyed at Klipfontein Dam