Floats attached to transducers have proved a popular solution and are used to measure the height of the float at the top of a reservoir. For large lakes even a change of 1mm represents a significant change in volume, so accuracy is essential. There are several installations of this type in mountainous areas of Italy. The use of submersible transducers in conjunction with 4~20mA output amplifiers enables signals to be communicated from remote measuring locations to a control room. Pressure transducers can be deployed to measure the ‘head of water’ from which depth can be calculated as an alternative monitoring method. In both cases RDP transducers are designed for long life delivering accurate and reliable measurement despite immersion in water.