Saving water saves the environment

This Issue This is a part of the Water heating and use feature

By - , Build 99

When you’re building a house, it’s relatively easy and inexpensive to include measures to save energy and water, which also saves money and the environment.

two tanks ready to install2
two tanks ready to install2

When we began designing a house for our property in Paekakariki a few years ago, saving water and power was a major focus. Paekakariki has a limited water supply from a catchment near the town. We wanted to try a more sustainable approach to urban living and were determined to reduce our consumption of energy and water.

The house was designed with the assistance of Melling-Morse architects of Wellington. It uses a passive solar energy design and features corridors on the northern side of the house with exposed concrete floors to store heat. Solar water heating was installed using an active system that circulates water through a panel. The system certainly helps reduce our power bill, but further gains could be made by increasing the panel area and including a timer switch on an electric backup so top-up heating is minimised.

Getting tanked up

After researching options for reducing water use, we decided that the best approach would be to use rainwater for non-potable water and the main supply for the remainder. We wanted the system to be easy to operate and to avoid cluttering the garden with above-ground tanks. Besides, a number of separate roof areas on the house would have made piping stormwater into above-ground tanks difficult. However, finding a practical option for buried tanks was challenging.

Standard plastic tanks can’t be fully buried and the only cost-effective concrete options were very large (22,000 litre) concrete tanks. These would have required a crane to lift and a very big hole to bury them in. The best option was to use two rectangular 4,500 litre plastic septic tanks which could be buried. These were easy to lift and bury with a small excavator.

The tanks are set up together, with the second tank slightly lower than the first. Once full, the first tank overflows into the second, which then overflows into a soak hole. A maintenance-free pressure pump (stainless steel and plastic) lifts water out of the tanks on demand to supply the laundry, toilet and outside taps. A separate plumbing system feeds these – with no connection to the mains, to avoid any risk of contamination. The two tanks feed into the pump inlet, with a gate valve on each tank inlet. The top tank is pumped first. If this runs out, valves are switched to the bottom tank.

Plenty of water and plenty saved

The 9,000 litres of storage, from our roof area of about 160 m2, has been plenty in most years. Based on our current usage, this storage gives us about 30 days’ use (from full if there is no rain). In dry years we have put a small amount of water into the tanks from the mains to get us through.

Kapiti Coast District Council (KCDC) is now looking at trialling an automatic top-up from the mains if tanks get very low. This would be easier for the householder, would keep draw-off rates from the mains system low, and avoid the risk of a pressure drop in the small Paekakariki system if everyone’s tank ran low at the same time.

We installed a water meter on the tank ourselves and asked KCDC to install one on our mains. In this way we have recorded our water use since the house was built in 2003. Over 955 days from December 2003 to August 2006 we used 263,682 litres (50.7%) from the mains supply and 256,759 litres (49.3%) from our rainwater tanks. The average daily usage for the family was 545 litres/day – of which 276 litres came from the mains and 269 litres from rainwater tanks. We are a family of two adults and two young children (the second arrived part-way through this period).

two tanks ready to install2

Low cost and low maintenance

The entire system of two tanks and a pump cost about $4,000. There was minimal cost involved with plumbing and burying tanks as these jobs were done during construction and little additional plumbing was required. This system has been very low maintenance. We probably lift the lid on the pump house once every 2–3 months at the most, and all that is involved is switching a valve and turning the pump on and off.

Such systems should be a normal part of any new home construction. Our local Kapiti District continues to grow in both population and water consumption. Providing high-quality treated water where non-potable water would do is costly to the whole community. It also has an impact on the local environment. The Waikanae River, from which the water for most of the district is drawn, is reduced to very low levels over summer. This affects the ecology and recreational value of the river downstream. It would be great to see the river levels increase if more people started saving water in this way.

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two tanks ready to install2
two tanks ready to install2

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