Is it safe to use rainwater?
Rainwater itself is considered to be pure. However, by the time it flows into a tank, it is likely to collect all types of contaminants including bacteria & viruses. If the water remains in the tank for some time, bacteria can grow in stagnant water, in pipelines and in some filters. Intermittent use of the water makes the problem worse.
How to treat rain water?
We can group rainwater contaminants info suspend particles and microbial contaminants like e-coli, bacteria and others. If the rain water is likely to be contaminated with other contaminants like lead or other materials, it will need additional treatment.
At a minimum, the first step is rainwater filtration, followed by adequately sized UV disinfection with a sufficient UV dose to inactivate all bacteria and other potential microorganisms.
Details of the rainwater treatment will depend on factors like
- Rainwater collection
- Likely rainwater contaminants
- End use of the treated rainwater
- Frequency of use of rainwater
- Peak flow rate of the rainwater through UV unit, etc.
UV disinfection of rainwater: Process Flow
Rainwater collection -> Storage tank -> Filtration -> UV disinfection
UV dose for rainwater disinfection
UV Dose of min. 30mJ/cm2 at the end of UV lamp life is generally considered the absolute minimum for secondary, non-potable use of rainwater.
Australian Drinking Water Guidelines, US EPA UVDGM and EU regulators specify minimum UV dose for drinking water >40mJ/cm2 at the end of UV lamp life.
The higher the UV dose, the better is the UV disinfection performance and there is generally no downside of a high UV dose.
If you have any questions about UV disinfection of rainwater, or if you would like more information, please feel free to call our friendly team on (02) 9896 1165 or email advance (at) advanceuv.com.au and we would be happy to help.