Although the ~duino project naming is starting to get a little out of hand, Nicoo created the Aquameterduino in order to track his domestic water usage. The purpose of measuring water usage with this project was to determine the usual amounts, so that irregularities in water use could be detected. The key to measurement was having a second water meter fitted with a reed switch that closed once per litre of water flowed through it.
Then it is a simple task of counting the pulses from this meter and working with the data via an Arduino board. Nicoo has added Ethernet access and a real-time clock module, and the data is sent to an online service such as cosm or can be polled over the network. The Aquameterduino is a prime example of what can be done with an Ethernet-enabled Arduino board, and to get started with your own version consider our Freetronics EtherTen - the Arduino-Uno compatible with onboard Ethernet, microSD socket and optional Power-over-Ethernet support, which would make powering a remote project a breeze:
To examine the project details, including circuits and code, see here.