Your address or property name:
Calculations use local rainfall data from:
Terry Hills NSW
Sydney (Observatory Hill)
Sydney Olympic Park
The rainfall station that is closest to the project site
Your roof area that can be connected to the tank
1. Roof area where water is collected (see info-button):
Specify the area of your roof (or other hard surface area) that is connected to your tank. To try to collect runoff from pervious surfaces such as lawns does not usually provide any major benefits, as runoff only occurs during long or intense rainfall events, that only accounts for a very small part of the annual rainfall. The majority of runoff ocurring in small, frequent rainfall events.
To simulate future increase in rainfall, simulate rainfall with a climate factor of:
If required, add
to simulate a future increase in precipitation (usually between 1.15-1.25).
One (1) means unmodified rainfall data is used for modelling. Values are entered in the format 1.25.
Click here to show/hide additional input for runoff calculations
Runoff is modelled with the first bit of rain being captured on the surface before runoff occurs, called
which is later lost through evaporation.
Inception losses (cracks, uneven surface etc.):
For impervious surfaces, enter the
. The first depth of rainfall equal to this value is retained in the surface before any runoff occurs, and this water is then lost as evaporation. Evaporation varies depending on time of year and is based on evapotranspiration data.
A value for initial loss of 0.5-1.0 mm is appropriate for roof areas, and 1.0-2.0 mm for surfaces such as roads and parking areas.
Inception losses evaporates according to season, but in maximum:
Specify the maximum time it takes for the initial loss to evaporate. Since evaporation is modelled based on evapotranspiration, during cold months there are times when no evaporation is modelled. Since evaporation still occurs even when there is no evapotranspiration a value of between 48 to 72 hours for each mm of initial loss should be entered.
Click here to show/hide additional entries for modelling systems in cold climates
Projects in cold climate - months where no runnoff occurs (frozen conditions and snow removal)
(Not ticked=No, no runoff occurs, Ticked=Yes, runoff occurs)
How would you use your rainwater?
1. Roof area where water is collected (roof, paved surfaces etc.)
2. Storage tank volume
4. Potential indoor water use (not drinking water)such as toilet flushing, indoor irrigation etc.
3. Outdoor area to be irrigated
2. Capacity of diversion to tank:
If there is a limited capacity in the diversion system from the catchment to the storage tank (in litres per second, can be limited capacity of roof gutters, pipes, pits etc.), specify this capacity.
A roof gutter can be assumed to have a capacity of about 1 L/s, if two gutters connect to the same downpipe from different sides the capacity is 2 L/s.
The capacity of a pipe depends on pipe dimensions and the grade of the pipe.
2. Storage tank volume:
Specify the size of the storage tank, volume that is available for reuse.
3. Outdoor area to be irrigated:
If water is to be used for outdoor irrigateon, specify the area that is to be irrigated.
4. Indoor water demand (not drinking water), for example toilet flushing or indoor irrigation:
The average water demand per day that does not need to be of drinking water quality and that can be supplied by reused water,
excluding outdoor irrigation
(this is modelled separately). This could be for toilett flushing, indoor irrigation or similar uses.
Approximate wateruse per fluch for a low-flush toilet is about 3 litres, and about 10 litres for an older toilet.
To calculate the average daily water demand for toilet flushing, multiply the estimated number of times the toilet is used per day with the number of litres per flush.
For other water use such as indoor irrigation, add the estimated number of litres used per day.
Do you want to enter more detailed data for the soil on you property? Then click here
If you do not know the soil properties on your own property, use the default values.
Depth of soil to be irrigated:
Specify the depth of soil that is to be irrigated.
Void ratio of soil:
Specify the porevolume of the soil that can fill with water before the soil is saturated.
Specify the field capacity of the soil. The field capacity the the maximum water holding capacity of the soil without water draining out through the bottom. Only part of the field capacity is available to the plants.
A good soil for growing vegetables or grass will have a field capacity of between 200-400 mm/m.
Available water (% of field capacity):
Specify the percentage of the field capacity that is available to plants. This is usually between 30-50%.
Crop factor Kc:
Specify the crop factor for the irrigated vegetation. Crop factor is multiplied with the average evapotranspiration to calculate the total evapotranspiration of the irrigated vegetation. A value of 1 represents grassed areas / parkland.
Irrigate when water level drops to % of available water:
Specify when irrigation is expected to take place. This is based on how much of the available water that is left in the soil. A large value of say 80% means irrigation will occur more frequently than if a smaller value, say 30% is specified.
Irrigate with a water volume equivalent to daily losses x :
Specify how much water is to be applied for each irrigation cycle, as a factor that is multiplied by the daily volume of water that is lost through evapotranspiration. This way irrigation depth is adjusted according to season. A factor of one (1) means that for each irrigation cycle the same amount of water is applied that is lost through evapotranspiration in one day. A small value means irrigation occurs more frequent but with a smaller irrigation depth while a larger value means a larger irrigation depth at a lesser frequency.
Water in excess of the water holding capacity of the irrigated areas can infiltrates to surrounding soil or drains out:
Infiltration capacity (hydraulic conductivity) of surrounding soil or equivalent drainage:
If water infiltrates to surrounding soil, specify the hydraulic conductivity (infiltration rate) of the surrounding soil (in mm/hour), or equivalent capacity of the drainage system.
This can vary depending on the type of soil that is present.
Approximate infiltration rates for different soil types are presented below.
Coarse sand 3600 mm/hr
Fine sand 360 mm/hr
Silt 36 mm/hr
Clay / sand 3.6 mm/hr
Clay / silt 0.36 mm/hr
Dense clay 0.00 mm/hr
Does your water usage change depending on the time of year? Click here to enter variations
Untick any months where no irrigation occurs (e.g winter)
(Not ticked=No, no irrigation occurs, Ticked=Yes, irrigation occurs)
Water demand per month, as % of
Indoor water demand
. 100% means that the value entered at 4. is used.
Water demand, not drinking water quality
differs depending on time of year, enter the percentage of average daily water demand depending on month. The value can reflect differences in water use throughout the year, for example for a holiday house. If no water at all is used, enter 0%.
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