On a recent overseas trip, I visited my cousin who lives in Germany. They live in a pretty village, part of a group of villages that come under the same local authority east of Frankfurt.
I asked what they do about storm water. They explained that under local authority regulations, every house has to have an underground cistern to collect and store rainwater and that all the downpipes from their roof feed into the cistern which is located on the property.
The cistern holds 6000 litres of water. It has a filter to trap any leaves or other matter
and a ballcock sensor that monitors the water level.
The principle is simple and effective. When the cistern is full, the ballcock sensor activates the overflow which allows the water to flow out of the cistern and into the authority’s storm water drainage system. This means that the storm water drains don’t get overloaded when there is a downpour, thereby reducing pressure on infrastructure and also downstream on lakes, rivers or treatment plants, wherever the storm water eventually goes.
Even smarter, there is an option – which my cousin has gone for – and that is to recycle the rain water. They have a pump installed in the house (it could also be outside or even in the cistern) which pumps rainwater out of the cistern and into the house where it feeds into pipes supplying the grey water system.
The rainwater is used to flush the toilets and to water the garden. It can also be used for washing clothes.
While the cistern has capacity, the sensor allows rainwater to be pumped into the domestic grey water system. When the water level in the cistern is too low, the cistern alerts the system indoors which switches from the cistern supply to the normal reticulated town water supply.
The economics are pretty straightforward too. Householders are charged for fresh water use and for rain/stormwater run-off, but there is a discount if you recycle your rainwater. The householder supplies the square meterage of their roof to the water authority so they can calculate a charge for rainwater runoff. If you have a cistern that recycles the rainwater, then the charge is not applied.
It’s a win/win/win/win – reducing demand on the water supply, reducing costs for the homeowner, reducing pressure on infrastructure and costs for the local authority and reducing the impact on the environment.
There are of course costs associated with installing the cistern and the grey water piping and pump in the house but these are up front costs that can be included in the building costs and they generate long-term savings.
It would be interesting to check with STURM, the German company that installed this rain water recycling and grey water system to find out what kind of costs are involved. This is the kind of strategy that we should be looking at adopting here in NZ.
STURM is the name of the company that installed this system
Their contact details are:
Phone: +49 (0) 74 54/97 69 00
Fax : +49 (0) 74 54/9 76 90 99
E-Mail: info (at) sturm-sulz .com
Some other useful links.
Wastewater treatment: A critical component of a circular economy
A paper given at the 8th World Water Forum held in Brazil in April 2018
“We need to transition from the linear model to a circular one focused on reducing water use and consumption and promoting the reuse, recycling, restoration and recovery of water resources”
Water recycling in Australia
Australian Water Association
“Recycled water can provide a reliable, climate-resilient and economically sound source of water, which can be an important component of a robust and resilient water supply system.”
Waste water recycling in Germany
DW Akademie – part of Deutsche Welle, a strategic partner of the German Ministry of Economic Cooperation and Development
“Germany leads the way in wastewater technology”