If you will use rainwater harvesting into a tank for washing your car, hosing hard surfaces, watering your gardens, then the quality of the water collected isn’t too much of an issue. Most roof surfaces are acceptable for outdoor uses, but if you will be drinking your tank water then you will need to ensure your rooftop is safe from pollutants.
In this article, we will tell you what roofing materials are safe and acceptable, portions of your roof when things might be present which you should avoid harvesting rainwater from, and maintenance to perform to increase the quality of your rainwater.
Acceptable Roofing Materials
Before harvesting rainwater for consumption, it is important to understand your roof, particularly what it is made from. Rainwater can be safely harvested off most roofing material types including Zincalume®, Colorbond®, galvanized steel and even undamaged asbestos. Roofing materials that should be avoided at all cost include exposed asbestos, lead, treated timber and bitumen and tar.
Asbestos that is unsealed, where fibres have been exposed, is hazardous. Some recommend sealing unsealed asbestos roof with a food-grade sealant, however I personally feel it would be safer to have it professionally removed and replaced.
An article published several years ago argued that there was widespread lead contamination in rainwater harvested in tanks. If true, there are more than two million Australians drinking rainwater and yet very few reports of lead poisoning. Nonetheless, rainwater can be polluted from rooftops where lead is present.
Lead can be found on rooftops where lead-based paints have been used, or more often in flashings on older roof types. Flashing are found at the found at junction of a roof. There is very good evidence that lead flashing is damaging to rainwater quality and so should be avoided. Where a lead flashing does exist on a roof collecting rainwater, then it should be removed as a priority. Thankfully, building controls today in Australia ensure new roofs are lead free.
Potential Contamination Hazards
In addition to avoiding hazardous roofing materials that will pollute your rainwater, there are certain structures on the roof that should also be fixed (if possible), or avoided including:
- Flues from heaters or furnaces
- Chimney pipes from wood burners
- Structures where birds often perch on your roof.
- Mounted appliances including air conditioners or hot water system which overflow or discharge water onto your roof.
Keeping Your Rooftop Clean
It is recommended as part of proper tank maintenance that you should inspect your roof and gutters every 3-6 months. Keeping them clean and your gutters free from leaves will help to protect your rainwater against pollutants including animal droppings, microorganisms, aerial chemical sprays, and air pollution (especially if in an industrial area, chemical plants and quarries).
If aerial sprays have happened in your area, or your roof is extremely dirty, before washing it down remember to disconnect your water tank. When cleaning or maintaining your roof take proper precautions and be safe:
- Have someone else present to help and/or keep watch.
- Avoid any power lines connecting to your rooftop.
If possible, it helps to cut back nearby trees that grow higher than your rooftops, or trim back branches that are nearby or overhang your roof. This reduces the leaves falling onto your rooftop and animals who might climb and scamper across your catchment area.
Accessories to Install for Higher Water Quality
Keeping your rooftop entirely clean is quite an impossible task, given wind will always blow dust on top of it, birds and insects fly by and so on. As such it is wise to install other accessories to keep your rainwater clean including:
- Inlet strainer – councils require these to prevent mosquitoes breeding in your tank water, and you can be fined if your tank isn’t properly screened.
- Water diverter – installing this device will prevent the first litres of rainwater flowing down your roof (often dirty water) from entering your water tank.
- Rain heads – a head piece with meshing often installed just below your gutter. They deflect leaves from while allowing rainwater to flow into the pipes leading to your tank.
- Gutter guards – meshing your affix to the top of your gutters to stop leaves, frogs and the like getting into them.
If you have found this article helpful for making your roof a safer area for harvesting high-quality rainwater, then all I ask is that you share it with at least one other person. Optionally, leave a comment below, or if you have a question to ask or something to contribute then please do.