Rainwater – Safety

Millions of people have lived long healthy lives drinking rainwater . . . . but that’s doesn’t mean that rainwater is entirely pure, or completely safe for everyone.


The following Chemicals are commonly found in rain: Hydrogen, Ammonium, Calcium, Magnesium, Potassium, Sodium, Suphur Tetroxide, Nitrus Oxide, Chlorine, Fluorine, Lead, Iron, Bromine, Manganese, Vanadium, Aluminium.

These chemicals are generally in safe, extremely low concentrations.


Rain pH is typically acidic, with a pH in the range around 5.0 – 5.6 9Neutral water is 7).

With local thunderstorms the pH can drop as low as 2.0.

The acidity is primarily due to the presence of the two strong acids in dilute form, sulfuric acid (H2SO4) and nitric acid (HNO3).

Although some of these contaminants are from pollution many of them are as a result of natural processes.

If nothing is done to reduce the acidity you can corrode the copper in your pipes. (See this link: ABC)

If you have concrete tanks the water should be neutral as the concrete leaches lime, which raises the pH.

However if you have plastic tanks you might like to consider adding a bag of limestone chippings to the tank, which also help to raise the pH.


Rainwater tanks are also likely to contain low levels of bacteria as a result of contaminants on the roof.

People who regularly drink this water will rapidly build up a resistance to the bacteria.

When people, who have no resistance to the bacteria, drink the water however there is a real chance of developing a gastro problem.

This is a particular concern if that person in very young, old, or already unwell.


Precautions you should take include

  • Rinse a new roof
  • Keep the roof clean and clear of leaves including removal of overhanging branches.
  • Screen the inlet and overflow of the tank with fine mesh to prevent birds, animals and insects getting in.
  • A well maintained leaf trap will reduce the amount of organic matter that enters the rainwater tank through the inlet.
  • The tank should be covered to prevent light from reaching the water as it will encourage the growth of algae and bacteria. The cover to allow access to the tank for cleaning and inspection should have a tightly sealed manhole.
  • Use only “food grade” plastic pipe and fittings.
  • Clean the gutters and tank inlet every three or four months.
  • Remove the sludge in the tank bottom every two to three years.

For cleaning and disinfection of tanks see Rainwater Problems

For Similar Posts see Sustainability