Water Efficiency Calculator for new dwellings
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Water Calculator
WC
Taps (Other)
Taps (Kitchen/Utility)
Baths
Dishwashers
Washing Machines
Showers
H2O softeners
Greywater
Rainwater
Installation Type
Unit of Measure
Capacity/Flow rate
(1)
Use Factor
(2)
Fixed use (litres/person/day)
(3)
Litres/person/day
= [(1)x(2)] + (3)
(4)
WC
(single flush)
Flush Volume (litres)
4.42
0.00
WC
(dual flush)
Full flush Volume (litres)
1.46
0.00
Part flush Volume (litres)
2.96
0.00
WC
(multiple fittings)
Average effective
flushing Volume
(litres)
4.42
0.00
Taps
(excluding kitchen/utility room taps)
Flow rate (litres/min)
1.58
1.58
Bath
(where shower also present)
Capacity to overflow(litres)
0.11
0.00
Shower
(where bath also present)
Flow Rate(litres / minute)
4.37
0.00
Bath Only
Capacity to overflow(litres)
0.50
0.00
Shower Only
Flow Rate (litres/minute)
5.60
0.00
Kitchen/Utility room sink taps
Flow rate (litres/minute)
0.44
10.36
Washing Machine
(Litres/kg dry load)
8.17
2.1
0.00
17.157
Dishwasher
(Litres/place setting)
1.25
3.6
0.00
4.5
Waste disposal unit
(Litres/use)
Present
3.08
0.00
Water Softener
(Litres/person/day)
1.00
0.00
(5)
Total Calculated use (litres/person/day)
=SUM(column 4)
(6)
Contribution from greywater
(litres/person/day)
(7)
Contribution from rainwater
(litres/person/day)
(8)
Normalisation factor
0.91
(9)
Total internal water consumption
= [(5)-(6)-(7)]x(8)
(litres/person/day)
(10)
External water use
5.0
(11)
Total water consumption (Building Regulation 17.K)
=(9)+(10)(litres/person/day)
Click here for instructions on entering data on WCs
WC Type
Effective Flushing volume* (litres)
(a)
Quantity (No.)
(b)
Total per Fitting Type
= (a)x(b)
(c)
Multiple Fittings?
Dual Flush?
1
Numbers only
Numbers only
Total (Sum of all Quantities) (d)
Total (Sum of all totals per fitting type) (e)
Average effective flushing volume (litres)=(e)/(d)
Click here for instructions on entering data on taps (other)
Tap Fitting Type
Flow rate (litres/min)
(a)
Quantity (No.)
(b)
Total per Fitting Type
=(a)x(b)
(c)
1
Numbers only
Numbers only
2
Numbers only
Numbers only
3
Numbers only
Numbers only
4
Numbers only
Numbers only
5
Numbers only
Numbers only
6
Numbers only
Numbers only
Total (Sum of all Quantities) (d)
Total (Sum of all totals per fitting type) (e)
Average flow rate (litres/min) = [(e)/(d)]
Maximum flow rate (litres/min) (f)
Weighted Average flow rate (litres/min) = [(f)x0.7]
Click here for instructions on entering data on taps (kitchen)
Tap Fitting Type
Flow rate (litres/min)
(a)
Quantity (No.)
(b)
Total per Fitting Type
=(a)x(b)
(c)
1
Numbers only
Numbers only
2
Numbers only
Numbers only
3
Numbers only
Numbers only
4
Numbers only
Numbers only
5
Numbers only
Numbers only
6
Numbers only
Numbers only
Total (Sum of all Quantities) (d)
Total (Sum of all totals per fitting type) (e)
Average flow rate (litres/min) = [(e)/(d)]
Maximum flow rate (litres/min) (f)
Weighted Average flow rate (litres/min) = [(f)x0.7]
Click here for instructions on entering data on baths
Bath Fitting Type
Capacity to overflow(litres)
(a)
Quantity (No.)
(b)
Total per Fitting Type
=(a)x(b)
(c)
Are there any showers present?
1
Numbers only
Numbers only
2
Numbers only
Numbers only
3
Numbers only
Numbers only
4
Numbers only
Numbers only
5
Numbers only
Numbers only
6
Numbers only
Numbers only
Total (Sum of all Quantities) (d)
Total (Sum of all totals per fitting type) (e)
Average capacity to overflow(litres) = [(e)/(d)]
Maximum Capacity to overflow (litres) (f)
Weighted Average capacity to overflow(litres) = [(f)x0.7]
Click here for instructions on entering data on dishwashers
Type of Dishwasher
Litres per place setting
(a)
Quantity (No.)
(b)
Total per Fitting Type
=(a)x(b)
(c)
1
Numbers only
Numbers only
2
Numbers only
Numbers only
3
Numbers only
Numbers only
4
Numbers only
Numbers only
5
Numbers only
Numbers only
6
Numbers only
Numbers only
Total (Sum of all Quantities) (d)
Total (Sum of all totals per fitting type) (e)
Average litres per place setting = [(e)/(d)]
Maximum litres per place setting (f)
Weighted Average litres per place setting = [(f)x0.7]
Click here for instructions on entering data on washing machines
Type of washing machine
Litres per kilogram of dry load
(a)
Quantity (No.)
(b)
Total per Fitting Type
=(a)x(b)
(c)
1
Numbers only
Numbers only
2
Numbers only
Numbers only
3
Numbers only
Numbers only
4
Numbers only
Numbers only
5
Numbers only
Numbers only
6
Numbers only
Numbers only
Total (Sum of all Quantities) (d)
Total (Sum of all totals per fitting type) (e)
Average litres per kilogram of dry load = [(e)/(d)]
Maximum litres per kilogram of dry load (f)
Weighted Average litres per kilogram of dry load = [(f)x0.7]
Click here for instructions on entering data on showers
Shower fitting Type
Flow rate (litres/min)
(a)
Quantity (No.)
(b)
Total per Fitting Type
=(a)x(b)
(c)
Are there any Baths Present?
1
Numbers only
Numbers only
2
Numbers only
Numbers only
3
Numbers only
Numbers only
4
Numbers only
Numbers only
5
Numbers only
Numbers only
6
Numbers only
Numbers only
Total (Sum of all Quantities) (d)
Total (Sum of all totals per fitting type) (e)
Average flow rate (litres/min) = [(e)/(d)]
Maximum flow rate (litres/min) (f)
Weighted Average flow rate (litres/min) = [(f)x0.7]
Click here for instructions on entering data on water softeners
Water softener consumption calculation for New Dwellings
Total Capacity used per regeneration (%)
(a)
Numbers only
The percentage value must be between 0 and 100
Water Consumed per regeneration (litres)
(b)
Numbers only
Average number of regeneration cycles per day (No.)
(c)
Numbers only
Number of occupants served by the system (No.)
(d)
Numbers only
Water consumed beyond 4% (litres/day) [1-[4/(a)]]x[(b)x(c)]=
(e)
Water consumed beyond 4% (litres/person/day) [(e)/(d)]=
Click here for instructions on entering data on greywater
The greywater collection calculation for New Dwellings
Bath, shower and wash
hand basin usage
(litres/person/day)
(a)
Percentage of used
water (a) to be
recycled (%)
(b)
Greywater available
for use (litres/person/day)
(c)=(a)x[(b)/100] (c)
Greywater demand
litres/person/day)
(d)
Greywater savings (litres/person/day)
Where (c) is greater than (d),(e)=(d),
otherwise (e)=(c)
(e)
Numbers only
Numbers only
The percentage value must be between 0 and 100
Demand calculation
For any appliance (WC, or washing machine) where grey water is to be used for supply to all of the appliances of that type within the property, the volume of water for grey water demand can be taken directly from the relevant appliance row. For any appliance (WC, or washing machine) where grey water is to be supplied to only a proportion of the appliances of that type within a property, the volume of water for grey water demand should be calculated according to an alternative methodology. This can be found in Appendix A16 of Part G of the Building Regulations 2010 (
available here
) and allows calculation of the water demand from only the appliances where grey water is to be used. The total volume of grey water demand calculated in accordance with either of the above methodologies (as appropriate) should be summed for WCs and/or washing machines and entered into Column (d)
Supply calculation
For any appliance (tap, shower or bath) where grey water is being collected from all of that appliance within the property, the volume of water for grey water supply can be taken from the relevant appliance row. For any appliance (tap, shower or bath) where grey water is being collected from only a proportion of the appliances within the property, an alternative methodology must be used. This can be found in Appendix A18 of Part G of the Building Regulations 2010 (
available here
) and allows calculation of the water use for only the appliances where water is being collected. The total volume of water available for grey water supply calculated in accordance with either of the above methodologies (as appropriate) should be summed for taps, baths and showers and entered into Column (a).
Savings calculation
The percentage of grey water collected to be recycled should be based upon manufacturers or system designer details of the system specified and be entered into Column (b). Where the grey water available for use is of greater volume than the grey water demand, the savings (litres / person / day) will be equal to the volume of grey water demand. Where the grey water demand is of greater volume than the grey water available for use, the savings (litres / person / day) will be equal to the volume of grey water use. This will be populated in Column (e), and this value transferred through to the relevant row.
Click here for instructions on entering data on rainwater
The rainwater collection calculation for New Dwellings
Rainwater Collected
(a)
Numbers only
Rainwater demand
(b)
Numbers only
Rainwater savings* (c)=(a)/(b)*(b)=
(c)
Rainwater collection
The water efficiency calculator for new dwellings methodology document available in Appendix A of The Building Regulations 2010 Part G (
here
) allows calculation of rainwater collection volume according to two methodologies, both of which are based upon BS8515:2009. These are outlined in Section A21 of the methodology document. The daily rainwater per person (litres) figure calculated by either method should be entered into row (a).
Rainwater demand
For any appliance (WC, or washing machine) where rainwater is to be used for supply to all of the appliances of that type within the property, the volume of water for rainwater demand can be taken directly from the relevant appliance row in Column (4). For any appliance (WC, or washing machine) where rainwater is to be supplied to only a proportion of the appliances of that type within a property, the volume of water for rainwater demand should be calculated according to an alternative methodology. This can be found in Section A26 of the water efficiency calculator for new dwellings methodology document (
available here
) and allows calculation of the water demand from only the appliances where rainwater is to be used. The total volume of rainwater demand calculated in accordance with either of the above methodologies (as appropriate) should be summed for WCs and/or washing machines and entered into Row (b).
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