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  Experimental method and theoretical calculations to
quantify savings through the use of water-efficient showerheads

Total savings through the sale and installation of Oxygenics showerheads since 2008 have been calculated by multiplying the number of units sold per month by the estimated monthly savings per unit (as per methodology below).   We have been careful to ensure a very conservative total estimate.
Experimental method (on-site testing)


To determine the probable financial, power and environmental savings through the replacement of a water-wasting showerhead with a water-efficient unit.


• water-wasting showerhead– Cobra Overhead Shower (Cobra code # 065) (25 LPM at 3 bar), as it is widely  
obtainable, has been in use for decades in South Africa and is still installed in hundreds of thousands of South  
African homes.
• water-efficient showerhead – Oxygenics Skincare (8LPM at 3 bar), as it is a quality unit widely sold in the USA
   and is ideally suited to South African conditions.
• geyser – Kwikot Dual 400kPa 100 litre, in an average domestic installation, without geyser blanket or lagged
• generic kWatt hour meter
• Cobra pressure regulator 400 kPa
• in-line generic flow control valve
• stopwatch
• bucket
• graduated measuring jug


In order to verify the accuracy of the calculations and the assumptions made, a field test was performed.

The scenario assumed was a family of four, each showering once a day for six minutes.

• A standard 100 litre 2 kW domestic hot water geyser was used, without a geyser blanket or plumbing
   insulation. The only draw of hot water from the geyser was for the timed showers
• Water pressure was approximately 320kPa and balanced between hot and cold
• The set point of the geyser was 65 C.
• Energy consumption by the geyser was measured over a number of 24 hour periods using a dedicated kWhr
   meter on the geyser electrical supply
• Water temperature at the showerhead was measured for both the high-flow standard showerhead and the
   water-efficient showerhead. The temperatures were 44 C and 46 C respectively, using a mix of hot and cold to
   result in a comfortable shower experience.
• The flow rate was established by measuring the volume of water issuing from the showerhead over 20 seconds
   (multiplied by 3 to get a LPM figure).

The electrical energy (kWhrs) used over successive 24 hours periods was measured

• with no water drawn from the geyser over the 24 hour period, to establish geyser standby losses
• with two 6 minute showers morning and evening (4 showers in total, amounting to 24 min of showering per
   day), using the water-wasting showerhead with a flow of 17.5 LPM. This flow rate could be achieved only by
   installing an in-line flow controller upstream of the showerhead, given that the unrestricted flow was over 25
   LPM, well over what can be taken as a South African average shower flow rate
• with two 6 minute showers morning and evening at approximately 7.5 LPM (total 4 showers and 24 min of   
showering per 24 hrs), using the water-efficient showerhead, rated 9.5 LPM at 550 kPa.

These tests were repeated for a number of successive 24 hr periods to ensure consistency of the results.


The figures obtained averaged to

• 17 kWhrs per 24 hours for the standard showerhead
• 9.5 kWhrs per 24 hours for the water efficient showerhead

Thus the saving was 7.5 kWhrs over the 24 hour period.

This is a very similar figure to that arrived at through calculation (8kWhrs).

Any differences between the calculated figures and the test results may be due to variations in the cold water intake temperature and ambient air temperature and therefore standing heat loss. The pipework heat losses were approximately 2kWatt hours per 24 hours in standby mode with no hot water used, and about 3kWatt hours per 24 hrs during the shower test periods, the extra 1kW of energy being that lost as the pipes were unlagged.

The figure given for the total number of kWhrs saved per year has been corrected for transmission line losses (approx 20%) between generating source and user.

The electrical energy used to purify water, pipe it to the home and back to the water-treatment plant, and to treat it at the plant, has not been included. This figure can range from 1-3 kWhrs per kL of water, depending on the municipality and plant (an average figure can be assumed to be 1.5 kWhr per kL). Hence the energy savings are even higher than calculated and measured.

For the water, carbon emission and other savings, please refer to Appendix B. These figures can be derived from calculations alone, rather than needing verification through experimental method.


It is clear that even in this conservative scenario of a family of 4, with a total of 24 minutes of showering per day, the savings of power, water and waste-water are truly dramatic. And the comparative savings and relative cost-effectiveness over other sustainable interventions are also remarkable.

The savings per household per showerhead are approximately

• R 4 000 annually on utility bills at current rates, with a return on showerhead investment (R200) of 18 days
• 97 000 litres of water (and therefore wastewater), enough to fill 3 medium sized domestic swimming pools
• 2 950 kW hrs of power, enough to supply the average South African home for approximately 7 months per year
• 4 tons of carbon emissions, equivalent to not driving ones car for ten months of the year
• 1.8 tons of coal with a reduction in all the associated localised ground and air pollution

Theoretical calculations to support the accuracy of test results from experimental method


The savings listed below are based on purely theoretical calculations using the following assumptions. The calculations are essentially the same as those used by the Eternally Solar Power and Water Savings Calculator.

Parameter Equation identifier Quantity
Water saving showerhead flow rate (L/M) L 7.5
Assumed water-wasting current shower flow-rate (L/M) A 18
Assumed average shower duration (Min) B 6
Number of showers per household taken per day C 4
Total water used for water wasting showers (L) A*B*C=TWW 432
Total water used for water efficient showers (L) L*B*C=TWS 180
Temp of shower water assumed – water wasting (C ) E 44
Temp of shower water assumed – aerated water efficient (C) S 46
Temp of hot water in geyser assumed (C) F 65
Temp of cold water from mains assumed ( C ) G 15
Temp elevation mains to geyser 20-60 ( C ) H 50
Energy required to raise temperature of 1 litre water by 1C (kWhr) I 0.001162
Flow rate of hot water for water wasting showerhead (L/M) ((E*A)-(G*A))/
Flow rate of hot water for water saving showerhead (L/M) ((S*L)-(G*L))/
Assumed hot water requirement (L) (for water wasting showers at 44 C) J*A*4=HWW 250
Assumed hot water requirement (L) (for water saving showers at 46 C) K*L*4=HWS 112
Electrical energy required at water wasting flow rate (kWhr) HWW*I*H=EWW 14.52
Plus energy lost through unlagged pipes (kWhr) EWW+2=EWWc 16.52
Electrical energy required at water saving flow rate (kWhr) HWS*I*H=EWS 6.5
Plus energy lost through unlagged pipes (kWhr) EWS+2=EWSc 8.5
Energy saved per day (kWhr) EWWc-EWSc=N 8.0
Electrical energy saved per year (kWhr) P*365=Q 2 928
Transmission line losses generation source to user (%) R 20
Total annual electrical energy saved at generation source (mWhr) Q+(Q*R)/1000=S 3.7

Some influencing factors

• Use of heat pumps in hotels and gyms to heat water can reduce power costs by about 60% by about 60%
• Temperature and length of showers varies widely, and we have used acceptable averages.
• Heat losses from pipework (as determined by field tests) have been factored in.
• Energy required for water purification, pumping, and waste-water treatment has not been factored into our
   calculator (it may be in an updated version), nor have the associated carbon emissions. Hence another reason   
why savings will be greater than calculated.

Water and Waste-water

The calculations for fresh and waste-water are straightforward in terms of volume, but the method of calculating rateable volumes and unit cost, of both fresh and waste-water varies from one municipality to another. The cost of waste-water also varies widely, and the default figures are based on Cape Town rates which represent an average.


Parameter Equation identifier Quantity

Current water-wasting shower flowrate (L/min)

A 18
Average Shower duration assumed (min) B 6

Number of showers per household taken per day C 4

Total water used for showers (L) A*B*C=D 432

Water saving showerhead flow rate (L/min) E 7.5

Water used at water saving flowrate (L) B*C*E=F 180

Water saved per day (kL) (D-F)/1000=G 0.25

Water saved per year (kL) G*365=H 92  

Parameter Equation identifier Quantity  
Fresh water daily savings (kL) A 0.25
Average proportion of fresh water volume that discharges to sewerage system (%)
B 90  
Daily waste-water volume saved (kL)
A*B=C 0.23  
Rating used by municipality to calculate chargeable vol. (%)
D 70  
Daily waste-water chargeable volume (kL) A*D=E 0.175  
In the Eternally Solar Savings Calculator, the bulk water savings include an additional figure, representing the
1.3 kL that Eskom uses to generate 1 mWatt of power. This gives a saving closer to 90 kL in the household scenario we have used

Cost Savings
Parameter Units saved Current avg. unit cost (R/kWhr
or kL)

  Cost saving  
Daily Annually
Power (kWhr) 6.7 R1.20 R8.04 R2 935  
Water (kL) 0.25 R12 R3.00 R1 095  
Waste-water (kL) 0.175 R10 R1.75 R639  
Sub-total     R10.45 R4 669  
VAT     R1.46 R654  
Total     R11.91 R5 323
Cost of average eco-showerhead       R200
Payback period (days) (R200/R4 094*365d)       14  

Carbon and Coal

Parameter Equation identifier Quantity  
Electrical power saved annually (mWhrs) A 3.0 A 3.0
CO2 emissions per mWhr generated (metric ton/mWhr) B 1.1
B 1.1  
Total CO2 emissions saved (metric tons) A*B=C 2.6
A*B=C 2.6  
Coal consumption (metric ton/mWhr) D 0.5
D 0.5  
Total coal volume saved (metric tons) A*D=E 1.45 A*D=E 1.45  

• Total energy savings are estimated at source, by multiplying savings by user by a transmission line
   loss factor (20%)
• Emissions figure used is 1.1 ton CO2 emitted per megawatt hour of electricity generated. The emissions may be  
as high as 1.1 ton per mWhr (source: Eskom), depending on the information source.
• Coal use is approximately 0.5 ton per mWhr of electricity produced (source: Eskom)
• Cost savings to South Africa would be very significant and could easily fund the wholesale installation of water-
   efficient showerheads – especially given that, apart from the infrastructural savings, the proposed tax penalty
   for emitting excess carbon imposed internationally would be reduced.


- 2007 Eternally Solar CC -

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