Preview Article: Water Friendly Homes

Preview Article: Water Friendly Homes

Water use efficiency is an increasingly vital issue, particularly when it comes to building new homes. Gary Workman from GreenPlumbers® has some advice for making households water-friendly…

The average Australian urban household consumes between 230,000 – 280,000 L of water per year. It is broken down as follows:

Garden use 35 – 50%
Bathroom 10%
Hot water 16%
Toilet flushing 10 – 20%
Laundry 10 – 20%
Kitchen 5%

A dual flush toilet reduces water use significantly

It is a wise idea to check with the local council during the planning stages when designing a new home. Most Australian states now have regulations for new home construction that include water and energy saving measures:

NSW – BASIX commenced 2004 (40% water and energy savings)
VIC – 5 Star commenced 2004 (internal water savings, plus either a 2,000 litre rainwater tank connected to all toilets or a solar hot water system)
QLD – Sustainable housing water and energy savings
SA – Sustainable housing water and energy savings

There are key areas in domestic homes where water savings can be made. The main water saving areas are:

1. Dual flush toilets – 6/3 or 4.5/3 dual flush toilet suites.

2. WELS – Water efficient labelled tapware and appliances. These include shower roses, dishwashers, clothes washing machines, laundry, kitchen and bathroom vanity tapware.


Solar hot water systems are environmentally friendly

3. Rainwater Tanks – What size Rainwater Tank do you need? Many state and local Governments mandate a minimum size of rainwater storage tank for new buildings and only certain sizes are eligible for many government rebate and incentive schemes. Check with the local plumbing/building authority for any rainwater storage tank sizing requirements. The following factors should be considered in determining the size of the rainwater tank for the intended use:


  • Rainwater performance – percentage % expectation of water supply to be sourced from rainwater
  • Rainfall for the region – rainfall data from Bureau of Meteorology, local rainfall stations, and council information.
  • Roof catchment size –sq/m of specific roof catchment area discharging to tank.
  • Allotment size – the available land to place tank in or on, the footprint size of the tank.
  • Is the network utility operators’ water supply available?
  • Water demand – intended use and daily water usage consumption.
  • Is stormwater attenuation to be incorporated into the rainwater tank? Stormwater attenuation is the temporary storage and slow release of stormwater to reduce flow rates into the stormwater drainage system during and immediately after a storm event. Local council requirements should be referred to.
  • Bushfire rainwater storage requirements – local council authorities may require rainwater storage tanks for the sole purpose of fire fighting.


Calculating Expected Annual Rainwater Catchment
There are a number of factors that need to be considered when calculating the expected annual rainwater catchment from a particular roof, or other harvesting areas, which will in turn help determine the size of the rainwater tank and the potential intended use.

These include rainfall for the region; rainfall data from Bureau of Meteorology, local rainfall stations and council; size of the specific roof catchment area discharging to tank;

pre-treatment devices (first flush, etc) that may divert rainwater away from the storage tank and the co-efficient run-off percentage from the catchment area. For example, an impervious surface such as a metal or tiled roof will have a higher coefficient runoff percentage than a grassed area, where a large percentage of water would be absorbed.

There is a tiled roof on a residential house in Sydney where a 70m2 roof area is draining to a single downpipe where they would like to capture and store the roofwater in a rainwater tank nearby. Rainfall for the Sydney region (1,217mm/year). Catchment size – sq m of specific roof catchment area discharging to tank (70m2). Coefficient runoff percentage from catchment area tiled roof – assume 90% coefficient rate for metal or tiled roofs. Pre-treatment devices – No device.

Answer: 1,217 x 70 x 90 = 76,671 litres per year of rainwater

To read the rest of this article, get the July issue of the Australian Hardware Journal in the Plumbing and Bathrooms feature.