We study the impact of audits on water conservation, distinguishing between the information and technological components. We observe water consumption for thousands of households in the South East of England for up to 18 months after they receive a visit of a so-called Green Doctor. We observe a decrease in water usage between 7.5 and 10 litres per day for each water-device and we find that this effect is persistent over 18 months. Devices reducing water pressure are particularly effective, while shower timers are ineffective. The information component of the water audit has a large initial impact of around 40 litres per day, but this effect gradually fades away over time, until it stabilizes to around 10 litres per day. Technology appears to be more cost-effective than information provision and this can help in the design of policy interventions. Co-authors: Carmine Ornaghi & Mirco Tonin.