Water efficiency
Reducing average pressures will also reduce some types of consumption. The instantaneous rate of consumption from devices connected directly to mains pressure will change with pressure. Examples include taps, showers and hose pipes - in particular garden irrigation systems. Many people irrigate their lawns at night, which in a system without Advanced Pressure Management, also coincides with the highest pressures.
If the water system in a property contains a header cistern (usually in the loft space), there will be little impact on consumption from pressure reduction. It is therefore important to know the predominant type of plumbing system in the area that is to be pressure managed.
The financial impact on the water company from this drop in pressure-related consumption depends on the proportion of metered customers in the DMA. In an area where customers are un-metered, the reduction in consumption will lead to a cost saving. However, where customers are metered, there will be a loss of revenue to be taken into account.
A method that can be used to predict the effect of average pressure on consumption is the FAVAD (Fixed and Variable Area discharges) equation, similar to the one used for leakage:
Any reduction in average pressure from P0 to P1 will cause a drop in consumption from C0 to C1. For internal residential consumption where the plumbing system is connected directly to the mains, a value for N3 of between 0 an 0.2 can be used. For external consumption such as lawn irrigation and garden watering, a value of N3 of 0.5 is more appropriate.