Rain water harvesting and energy use

May 5 by : admin

Analysis by the Office of Living Victoria showed the amount of rain that hit some homes last year was the equivalent of almost $400 in drinking water if it had come out of the tap.

But while we have the figures to prove that rainwater tanks can save a lot of water, there are some who may be concerned about the extra energy required to pump the harvested rain water for use in and around the home. Gravity may be the most efficient way of delivering rain water to taps, but it is not always feasible. As a result most households have to install small pumps with their rainwater tanks that would switch on every time the tap is turned on.

Are we saving money by harvesting rain water but spending the savings to use it? The good news is, research findings have showed that the savings far outweigh any increase in energy use.

Water savings

In 2011, Sydney water conducted a 12-month study on rainwater tank water savings and energy use for 52 real life installations. They discovered that rainwater tanks installed as required by NSW water efficiency regulations are, in the majority of cases, saving an average of 39 kL of water per household per year (or 20% of household demand) and up to 96 kL per household per year.

The study found that harvested rain water is meeting approximately 60% of rainwater tank-connected demands and that rainwater tanks are reducing drinking water use from mains supply in these households by on average 21% by substituting rainwater for drinking water for alternative water uses. Most importantly, rainwater tanks are helping the households in the study successfully reduce their water use to below 200 kL per year.

Energy usage

When it comes to energy usage, research conducted by the Institute for Sustainable Futures at the University of Technology, Sydney, found that there are ways to minimise energy demand from rainwater tanks through careful design, configuration and calibration of pumps and rainwater tanks. The position of the rainwater tank in the house and its connection to likely uses have a further bearing on energy usage.

Most significantly, however, are the findings from Sydney Water’s study, which found that on a single household perspective, rainwater tank pumps consume only a small amount of energy. The average energy use of 78 kWh/year or approximately $20 per year is only a small percentage of energy costs for a household and is more than offset by the water cost savings ($400).

So don’t let the fear of spending a little more money on energy deny you the greater savings from harvesting rain water.