Freshwater
is essential to human existence, and to the functioning of the ecosystems that
support us. Australia is the driest populated continent on earth and can yield
only a limited amount of freshwater. The average annual rainfall in Australia
of 469mm a year is well below the global average. Despite this, Australians are
the greatest per capita consumers of water, using an average of 100,000L of
freshwater per person each year. This figure increases tenfold if the water
embodied in the food and products we consume is included.
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Available freshwater resources are expected to decline with changes to rainfall patterns accompanying global climate change. As our population grows, so does the pressure on water use. To ensure future supplies of fresh, clean water we need to use it more carefully.
In addition to the problems of limited supply, the way we use water contributes to a range of ecological problems. Conserving water resources, even in areas without shortages, helps reduce the need to build dams, protects river health by reducing the need to extract water, reduces wastewater produced and treated at sewage plants, lowers energy requirements for treating and transporting water and wastewater, and reduces greenhouse gas emissions. Managing surface runoff and stormwater pollution helps to prevent the degradation of rivers, wetlands and oceans.
The two big issues that households can help to address are:
Homes and gardens are directly responsible for about 12% of Australia’s water use and much can be done in the home and garden to reduce water use and the impacts of stormwater and wastewater.
Australia is the driest populated continent on earth, and yet Australians are the greatest per capita consumers of water in the world.
In addition to the problems of limited supply, the way we use water contributes to a range of ecological problems. Conserving water resources, even in areas without shortages, helps reduce the need to build dams, protects river health by reducing the need to extract water, reduces wastewater produced and treated at sewage plants, lowers energy requirements for treating and transporting water and wastewater, and reduces greenhouse gas emissions. Managing surface runoff and stormwater pollution helps to prevent the degradation of rivers, wetlands and oceans.
The two big issues that households can help to address are:
- Reducing the quantity of water we consume
- Improving water quality by managing stormwater and wastewater.
Homes and gardens are directly responsible for about 12% of Australia’s water use and much can be done in the home and garden to reduce water use and the impacts of stormwater and wastewater.
Australia is the driest populated continent on earth, and yet Australians are the greatest per capita consumers of water in the world.
reducing water demand
Reducing
water consumption in the home is a simple and easy way to decrease water and
energy bills and reduce your household’s impact on the environment. Indoors,
the shower is typically the biggest water user (34% of indoor water use in the
average Australian home), followed by the toilet (26%) and laundry (23%).
Therefore, effective strategies include choosing water efficient showerheads,
toilets, appliances and taps. Outdoors, strategies include choosing local
indigenous plants that are adapted for local growing conditions, mulching, and
using water efficient irrigation systems.
New homes can be designed to be water efficient and in existing homes water demand can be reduced with renovations and minor upgrades. The national Water Efficiency Labelling and Standards (WELS) scheme requires certain products sold in Australia to be registered, rated and labelled for their water efficiency. Look for the WELS label as a guide for choosing showerheads, toilets, washing machines, dishwashers and taps. It contains a star rating (the more stars, the more water efficient the product) and data on actual water consumption.
New homes can be designed to be water efficient and in existing homes water demand can be reduced with renovations and minor upgrades. The national Water Efficiency Labelling and Standards (WELS) scheme requires certain products sold in Australia to be registered, rated and labelled for their water efficiency. Look for the WELS label as a guide for choosing showerheads, toilets, washing machines, dishwashers and taps. It contains a star rating (the more stars, the more water efficient the product) and data on actual water consumption.
rainwater
Using rainwater
can reduce your water bills, provide an alternative supply during water
restrictions and help maintain a green, healthy garden. It can also help to
conserve water resources and reduce environmental impacts beyond the home.
Rainwater collected from a well-designed and operated system can be suitable for all domestic uses. The more uses, the greater the savings in mains water. Different |
uses (e.g. toilet flushing, showering) require different levels of treatment. A typical strategy is to use rainwater for the garden and some indoor uses such as toilet flushing, clothes washing and even showering, while sourcing drinking water (which requires the highest level of treatment) from a mains water supply. Typical components of a rainwater system include the roof and gutters, collection system (rain-heads, downpipes and first flush diverters), tank and supply system (pumps, controllers and filters).
Optimum tank size depends on a number of factors including how many uses the rainwater supplies, local rainfall characteristics and roof catchment area. Rainwater systems must be designed to minimise health and safety risks, and need to be maintained.
Optimum tank size depends on a number of factors including how many uses the rainwater supplies, local rainfall characteristics and roof catchment area. Rainwater systems must be designed to minimise health and safety risks, and need to be maintained.
wastewater reuse
At present,
potable (drinkable) water is used for practically everything in the house and
garden. We are literally flushing our drinking water down the toilet! On-site
wastewater reuse can reduce potable water use in the home, though the
opportunities for reuse vary depending on where you live. The two types of
wastewater created in a home are greywater from non-toilet plumbing fixtures
such as showers, basins and taps, and Blackwater which has waste from the
toilet.
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Grey water is ideal for garden watering if detergents low in sodium and phosphorus are used and it is applied below the surface. Appropriately treated greywater can also be reused indoors for toilet flushing and clothes washing, both of which are significant consumers of water. Blackwater requires biological or chemical treatment and disinfection before reuse. For single dwellings, treated and disinfected Blackwater can be used only outdoors, and often only for subsurface irrigation. Your local council or state health department can advise on local requirements.
The options for wastewater reuse vary and each has advantages and disadvantages, as do the types of wastewater treatment systems.
The options for wastewater reuse vary and each has advantages and disadvantages, as do the types of wastewater treatment systems.
stormwater
Stormwater
is all rain that falls on the roof or land plus anything it carries with it as
it drains off site. Stormwater that carries soil, organic matter, litter,
fertilisers from gardens and oil residues from driveways can pollute downstream
waterways. Reusing stormwater can save potable water and reduce downstream
environmental impacts.
Stormwater impacts can be managed during building construction and through water sensitive landscape design. Strategies to employ during construction include limiting cut and fill, and retaining existing vegetation on site (see the appendix Sediment control). Landscaping approaches follow the principles of water sensitive urban design, which seeks to imitate the natural (pre-development) water balance of the site. Strategies include permeable paving, garden beds designed for infiltration, and landscape features (e.g. swales and soak wells) that detain stormwater and increase percolation into the soil.
Stormwater impacts can be managed during building construction and through water sensitive landscape design. Strategies to employ during construction include limiting cut and fill, and retaining existing vegetation on site (see the appendix Sediment control). Landscaping approaches follow the principles of water sensitive urban design, which seeks to imitate the natural (pre-development) water balance of the site. Strategies include permeable paving, garden beds designed for infiltration, and landscape features (e.g. swales and soak wells) that detain stormwater and increase percolation into the soil.
outdoor water use
Around 40%
of household water is typically used outdoors, and in some locations in
Australia the proportion is much higher. Using water conservation techniques in
the garden saves money, time and effort and benefits the natural environment.
The many easy ways to reduce outdoor water use follow the principles of water efficient garden design and include choosing plants adapted to the local climate, improving the condition and moisture retention of soil, maintaining the garden, and using water-saving garden products and efficient irrigation systems. (See the appendix Landscaping and garden design)
The many easy ways to reduce outdoor water use follow the principles of water efficient garden design and include choosing plants adapted to the local climate, improving the condition and moisture retention of soil, maintaining the garden, and using water-saving garden products and efficient irrigation systems. (See the appendix Landscaping and garden design)
waterless toilets
Around 40%
of household water is typically used outdoors, and in some locations in
Australia the proportion is much higher. Using water conservation techniques in
the garden saves money, time and effort and benefits the natural environment.
The many easy ways to reduce outdoor water use follow the principles of water efficient garden design and include choosing plants adapted to the local climate, improving the condition and moisture retention of soil, maintaining the garden, and using water-saving garden products and efficient irrigation systems. (See the appendix Landscaping and garden design) |
The different types of waterless toilets work differently and have different maintenance requirements. There is one just right for your home.
Rainwater harvesting means capturing and storing rain that falls on-site (usually on roofs). It is generally used for irrigation and toilet flushing or other greywater uses, though it can also be used for drinking water if it is adequately treated.
Rainwater harvesting means capturing and storing rain that falls on-site (usually on roofs). It is generally used for irrigation and toilet flushing or other greywater uses, though it can also be used for drinking water if it is adequately treated.
Capturing rainwater can be a valuable way to reduce or even eliminate a building's use of municipal potable water, without requiring reductions in water use by occupants. However, it is of course more effective in rainy climates than dry ones.
Rainwater harvesting systems are measured by their area for collecting water (in m2 or ft2) and the volume of water they store (in litters or gallons).
Simple rainwater collection systems have three main elements: the roof or other catchment area, the storage tank(s), and the gutter and other piping that directs the water from the catchment area to the tank.
Rainwater harvesting systems are measured by their area for collecting water (in m2 or ft2) and the volume of water they store (in litters or gallons).
Simple rainwater collection systems have three main elements: the roof or other catchment area, the storage tank(s), and the gutter and other piping that directs the water from the catchment area to the tank.
Advanced
systems may also use a pump to pull water from the tank to where it is used,
and may purify the water with additional devices such as filters and ultraviolet
disinfection.
If the rainwater is meant for drinking or watering gardens, be sure to choose a tank material that does not leach toxins or foster pathogens. For example, galvanized steel tanks are lined with polyethylene or other food-grade liner.
If the rainwater is collected from a roof is meant for drinking or watering gardens, be sure to choose roofing materials that do not leach toxins. For instance, asphalt shingles leach toxins into water, while metal roofs or slate shingles do not.
If the rainwater is meant for drinking or watering gardens, be sure to choose a tank material that does not leach toxins or foster pathogens. For example, galvanized steel tanks are lined with polyethylene or other food-grade liner.
If the rainwater is collected from a roof is meant for drinking or watering gardens, be sure to choose roofing materials that do not leach toxins. For instance, asphalt shingles leach toxins into water, while metal roofs or slate shingles do not.
predicting rainwater harvest rate
To size a
system for a site, you must choose the water collecting area to supply enough
volume of water for the site occupants, given the site's rainfall
patterns. The simplest equation for
system sizing is this:
(Volume) = (Area) • (Precipitation) • (% Efficiency)
Volume is the amount of rain harvested in that time period, measured in litters. Area is the rainwater capture area, measured in m2. Precipitation is the amount of rainfall in that time period (in mm). Efficiency is the percent of water actually captured, as opposed to splashing out of the system somewhere; it is usually 75% - 90%.1
In English units, a coefficient must be added:
(Volume) = (Area) • (Precipitation) • (0.62 gal/ft2/inch) • (% Efficiency)
Here volume is in gallons, area is in ft2, precipitation is in inches.
(Volume) = (Area) • (Precipitation) • (% Efficiency)
Volume is the amount of rain harvested in that time period, measured in litters. Area is the rainwater capture area, measured in m2. Precipitation is the amount of rainfall in that time period (in mm). Efficiency is the percent of water actually captured, as opposed to splashing out of the system somewhere; it is usually 75% - 90%.1
In English units, a coefficient must be added:
(Volume) = (Area) • (Precipitation) • (0.62 gal/ft2/inch) • (% Efficiency)
Here volume is in gallons, area is in ft2, precipitation is in inches.
occupant needs
The volume
of water needed by the occupants will vary based on the number of occupants,
the amount of time they spend on site, the activities they engage in, and the
equipment or processes used on site.
These needs are often constant throughout the year, but if they vary by season, be sure to incorporate that in your calculations.
These needs are often constant throughout the year, but if they vary by season, be sure to incorporate that in your calculations.
rainfall
Weather data
from TMY files can be used to determine rainfall patterns. These will be in mm or inches of rain.
Be sure to calculate average monthly rainfall for the different months of the year, not simply an annual total. Most sites have much more rainfall in some seasons than others, and excess water can always be drained, but a lack of water requires municipal water use to compensate.
Be sure to calculate average monthly rainfall for the different months of the year, not simply an annual total. Most sites have much more rainfall in some seasons than others, and excess water can always be drained, but a lack of water requires municipal water use to compensate.
efficiency
Different
gutter systems, different roof pitches, and different materials can affect
system efficiency. For example,
lower-pitch roofs cause less loss than steeply-pitched roofs.
sizing rainwater tanks
There is no
one standard recommended size for rainwater storage tanks. The size depends on the site's water needs,
the weather, and whether the site is connected to a municipal water supply or
not. While bigger tanks allow for more
water independence, the tank is usually the most expensive part of the system.
Systems that do not have municipal water backup (called "off-grid") must hold much more water, in case of shortage. The amount of oversizing depends on how crucial the water needs are--discretionary water use like lawns or water features can be done without for days or weeks at a time, while drinking water cannot.
The main consideration for sizing a storage tank is the worst-case length of time between rains. This can be seen by graphing the TMY precipitation data by day, rather than simply finding monthly precipitation averages. After you have calculated the occupants' water needs and the average frequency and magnitude of rain in the dry season, you should multiply the resulting tank size by a "safety factor" to provide room for error or extreme weather.
Systems that do not have municipal water backup (called "off-grid") must hold much more water, in case of shortage. The amount of oversizing depends on how crucial the water needs are--discretionary water use like lawns or water features can be done without for days or weeks at a time, while drinking water cannot.
The main consideration for sizing a storage tank is the worst-case length of time between rains. This can be seen by graphing the TMY precipitation data by day, rather than simply finding monthly precipitation averages. After you have calculated the occupants' water needs and the average frequency and magnitude of rain in the dry season, you should multiply the resulting tank size by a "safety factor" to provide room for error or extreme weather.