- Make sure your roof surface is suitable for collecting quality rainwater. Some roofs are composed of lead-based paints and flashing, and tar-based coatings. Be certain that your roof is non-toxic. Steel sheets, well fired glazed tiles, concrete or cement tiles, clay tiles, and composite tiles are popular choices safe for rainwater collection.
- Speak with the manufacturer to confirm that the roofing material is suitable for potable water collection. You can obtain a certificate of classification.
- Install roof gutters according to appropriate standards and building codes. Be aware that gutters which pond water can create a mosquito breeding habitat and may incubate bacteria.
- Prevent leaves and debris from blocking gutters by installing a fireproof mesh gutter system. Screening material must be both fire proof and allow maximum sunlight into the roof gutter system. It also must not be too fine, which can create the perfect habitat for spiders.
- Fit gutter outlets on the underside of the roof to minimize sludge build up. Gutter outlets that are fitted from inside the roof create a lip of up to 4mm at the water outlet point. Instead, fix gutter outlets on the underside of the gutter itself, so there is no water flow obstruction and the gutters will drain well.
No leaves, debris, or bugs please!
- Rain heads direct leaves and larger debris out of the flow of the water. The type of rain head required depends on the type of system. Using ‘multiple screen’ rain heads is often the best strategy.
- Consider using dry gutters. They last longer, keep the water moving downward, and prevent water accumulation between flushes. Dry gutters also eliminate any breeding ground for mosquitoes.
- In wet systems, pipes and gutters hold water. Fit insect-proof screens on all pipes that hold water and all openings to or from your tank. You can also fit insect-proof flap valves or screens on the end of the pipe system at the entry to the rainwater tank, and to the overflow from the tank.
- Install a first flush diverter on the downpipe. This is critical for achieving good quality water and is especially important in areas of high pesticide use or atmospheric pollution.
- First flush water diverters prevent the first, most contaminated rainwater from entering the tank.
- The recommended volume to be diverted is based on an assessment of roof area, and a pollution factor (between 0.5L to 2L of water per m2 of roof area).
- A sump box between the downpipe and the tank can slow water flow down and separate out any sediment not previously diverted.
- Match the size of your tank to your water budget, your financial budget, and available space.
- Make sure your tank is made of dark, nontransparent material. Light will stimulate the growth of algae in stored water. Where an algal problem already exists, it is best to drain the tank and clean it.
- Tanks should be positioned in a shady spot, preferably away from trees to prevent leaves, etc., contaminating water.
- All openings should be equipped with close fitting lids, or mesh screens.
- All openings should be screened so that the mesh gauze will fit on a collar about 50mm deep. This will allow effective water flow into the tank. Ensure that screens are mosquito proof.
- Ensure that screens and filters are positioned so they are accessible for cleaning.
- Avoid brass or copper screens as they may react with the galvanising of the tank.
- Make sure there is an overflow valve on the tank outlet
- A close fitting lid which is readily removable is recommended.
- If you plan to have a large tank, consult a licensed builder or engineer to help design and construct the proper structural support.
- Have your tank installed by a plumber or the tank manufacturer. This will ensure the system operates efficiently, validate any available warranties, and lead to easier maintenance.
Water at the bottom and water at the top
- Draw water out of the tank from two places. Water at the top of the tank is better quality.
- Install a valve at least one third of the way from the top of the tank (aerobic zone) for use inside the home, and the other valve at the bottom of the tank (in the anaerobic zone) for use outside the home and overflow. Tank overflows that simultaneously take excess water and vacuum out sludge from the bottom of the tank are best.
- Make sure the tank overflow outlet is connected back into the stormwater pipe or irrigation system.
- Aerate the tank water so it does not become stagnant.
- Vent pipes and tanks to provide airflow over the water surface, which improves its aerobic content. This also prevents a vacuum from forming when large quantities of water are quickly drawn from the tank.
- Flap valves should have double seals, be self-cleaning, and have a flap that cannot be over-rotated and left open.
Keep the system in order
Maintenance is one of the most important factors to ensure good quality water. Clean the inside of the tank every few years, as sediment will accumulate. All components, including gutters, rain heads, water diverters and water tanks, should be checked and maintained regularly. Also, consider registering your rain harvesting system with the proper local officials.
The Rainwater Glossary:
Rainwater harvesting guide: