It is tempting to believe that by draining 10 gallons of greywater by gravity to a few mulch basins with a tree in each, is actually saving 10 gallons of potable water.
It probably isn’t. If the trees combined only needed a total of 3 gallons per day, that’s all that has been saved. The remaining 7 gallons has been lost via evaporation and drainage.
In many cases branched drain and laundry to landscape systems are massively overwatering the target plants. So while it is nice to look back at the system and believe it is saving water, the actual water save can be as little as 20% of the water collected.
Compare this to a properly calculated irrigation system – because it is 90+% efficient, and replaces a 50 – 70% efficient potable system, a gallon collected can save between 1.5 and 1.8 gallons of potable water.
About 20 years ago, a couple of early greywater DIY experimenters tried using pumps to distribute greywater. Unfortunately the technology was very basic, and systems failed quickly.
Consequently, a cottage industry developed over time that still avidly disavows anything to do with pumping greywater – especially at the residential level.
20 years is a long time, and the basic technological requirements (pumping, filtration and dispersal) are now served by time-proven and relatively inexpensive components.
- While gravity driven irrigation systems (especially greywater dripperlines) are inexpensive and highly efficient, the ideal system for whole of house graywater re-use, (and certainly where the irrigation field/s are uphill from the greywater source), a pumping station will be required. In the past these were expensive, but quality products are now available for around $500-$600.
- Tens of thousands of greywater pumping and irrigation systems have been installed in the hot and dry Australian climate, without requiring significant maintenance. More and more pumped systems are now manufactured and installed in the US without any issues.
Some of the sillier claims still promoted on current websites are:
- Pumps don’t work long without filtration.Dirty water submersible pumps are designed for …dirty water. They use an impeller to create a whirlpool in the pump and force the water out with little contact with the impeller.
They are designed to pump soft solids up to 1 1/2″ or more in size. About 10 years ago there was a common perception that greywater had to be filtered before the pump, to preserve the pump.
This has since been proven false – in over 6,000 systems manufactured and sold Just Water Savers USA & Just Water Savers (Australia), not one pump has been bound by hair or lint, and this is with filtration after the pump.
- Pumps use a lot of electricity, typically being between the number 2 and 5 energy consumer within the home.A 660 Watt pump, providing more than enough power for residential greywater applications, will typically run for 1/2 hour per day, in total, with 4 people living at the house, and actually only uses 450 Watts during operation. Therefore the total daily power usage is 0.25 kilowatt hours.
At say, 11 cents per kilowatt hour (2007 USA average), this comes to a cost of 2.8 cents per day, or $6.70 per year (60.8 kWh). As comparison, this is less than the amount of power consumed by a DVD player, hardly in the top 5 energy consumers in the home.
- California already uses too much electricity for pumping water, we should discourage use of pumps on-site when reusing water.The is one of those “I can’t believe they say that” claims.
A pumped irrigation system uses 10% of the power the water companies used to deliver the water to your property in the first place. So if you continue to use water company supplied water to irrigate instead of efficiently reusing on site, you are now using 90% more power than necessary.
We have the numbers and calculations for this, but most people aren’t that interested. Contact us if you would like the detail.