“The key issue is that good design based on real historical knowledge avoids most of the perceived maintenance problems – a high level of costly (and unnecessary) maintenance to counter marginal/ill-informed design choices is a very poor outcome indeed”.
Dr. Peter Coombes, March 2014, Sydney RHAA Breakfast.
Good design is a simple way to ensure rainwater is healthy, clean, clear and doesn’t smell. Rainwater comprises a low public health risk and is drunk by over 2 million mainly rural Australians every day. By considering the whole system and looking at potential problems any system can be designed to maintain high quality water. By designing multiple barriers through the rainwater harvesting process, for example gutter guards as well as a leaf diverter, water quality is improved through the process and water quality is protected even if one of the barriers fails.
A Quality Management Process for Rainwater Harvesting Design
- Assess the site and location specific contamination risks. The obvious ones are leaves from nearby trees and air pollution if you are in an industrial or rural area or near a busy road.
- Design, install and operate the rainwater system to provide progressive sequential redundant barriers to collection and distribution of contaminants.
- Each stage in the sequence of water collection, storage and distribution will be designed to enhance yield and water quality – contaminant loads will be continually reduced – over reliance on later stage filtration and disinfection is not recommended.
- Ensure equipment and materials in system are suitable for use
- Monitor water quality and respond rapidly if changes in water quality are observed (this may be limited to just clarity, colour, smell and taste)
Such a framework encapsulates a systems approach giving system designers some rules of thumb to guide design. (Rain Harvesting Group, 2014)
Managing quality using safeguards
- Rooftop – reduce or eliminate overhanging vegetation and fauna access, eliminate (or seal) materials which may leach hazardous chemicals for example lead from lead flashing, solder, nails, paint on old roofs and gutters
- Gutters – gutter guards prevent moist vegetation from providing microbial breeding grounds and reduce organic matter entry into water storage
- Pollutant traps and leaf diverters – reduce organic nutrients into rainwater tank and charged lines and provides mosquito screening for charged lines
- First Flush – reduce/divert dissolved and fine suspended contaminants including faeces, dust, settled airborne particles (diesel particulates, pesticides etc) and heavy metals (mainly in industrial areas) collecting in rainwater tank. The only treatment points for small suspended particles and dissolved contaminants are the first flush system and sequestration into rainwater tank sediments.
- Preventing stagnation (by reducing organic matter entry) and or manual or self-draining discharge of charged systems reduces likelihood of stagnant water entry into tank .
- Rainwater tank sealed to prevent animal entry, back flows of water, mosquito entry and algae growth. Avoid re-suspension by use of calmed inlet and upturned outlet 100mm from base of tank. Avoid sediment suction by floating off take with collar, placement of submersible pumps on a stand or positioning pump outlet 100mm above base of tank.
This is one of a series of blogs to promote the new maintenance section of the Rainwater Harvesting Association website.
The Rain Harvesting Group is a member of the Rainwater Harvesting Association of Australia