 There is evidence from the UK that there is an instant drop in consumption of some 10% when meters are installed, although in most instances consumption isn't directly measured prior to meter installation, so the benefits are uncertain.Whilst metered water users in the UK do use less than unmetered users, in most areas metering is not compulsory, so the metered customers are a self-selecting group.There is also concern that water metering could be socially regressive, as householders on low incomes are less able to invest in water efficiency measures and may experience water poverty (defined as when a household spends more than 3% of net income on water and sewage services).