A central component of forecasting is extrapolation – that is, assuming that the trends of the past will continue into the future. The science of this process has become more sophisticated with time. Forecasters are increasingly using demographic characteristics to predict how and where demand will change. Forecasts offer the means through which the potential impact of different measures for influencing demand can be evaluated. For example, in their evaluation of means of reducing water demand in the UK, P. Sim and his colleagues concluded key factors enabling a moderation in demand would be the spread of metered charging and, to a lesser degree, the diffusion of water-efficient devices including washing machines, low-flow taps and low-flow showers. Regulations are absolute rules prohibiting the use of specific behaviours or technologies. The most extreme or enforced form of regulation is rationing, involving physical restrictions on the time that water can be accessed or the extent that can be obtained.