Water and Gravity

Building a home on a lot means consuming open ground. Open ground is essential for absorbing water, so less ground means less chance to absorb water from rain and snow. This means that the water that accumulates needs to be dealt with in another way. In most cases this water is funnelled with the use of gutters, downspouts and sloped driveway slabs to a storm water system run by the town or city.  This causes a burden on the town or city. The idea of requiring each new home to deal with its own accumulating site water rather than relying on the town or city is a growing requirement for many jurisdictions.

While we have provided on site dry wells (gravel pits buried in the ground to capture the water and allow it to be dispersed back into the town’s storm water system at a slower rate), we have gone one step further and provided a water storage tank buried below ground. The water that we are able to gather and store will be used for watering our garden.

The tank we used is from Premier Plastics and is a 4000 litre tank buried at the side of the house. In terms of how much water we can expect to accumulate and use, Outland Design did the following analysis:

 

• We have the potential of collecting 5800 litres of water from rain runoff from the roof and walk way areas (based on environmental information and roof area).
• With a garden area of 5 m2 which would require watering at 25mm per week, the volume of water required would be 0.125 cubic meters or 125 litres per week.
• With a 4000 litre cistern we will be able to provide water for approximately 32 weeks or 8 months of the year.

The benefit of our sloping site also allows us to use gravity to make all of this work. No pumps required. Water drains from the roof and site down into the tank in the ground. The garden area is below the tank on the lower tier of the lot which allows the water in the tank to flow down to the garden area. There are some extra costs to this system, but the benefits of having a water supply that is not tied to drought restrictions imposed by the City, and making use of the water gathered rather than paying for it, have their benefits.