Water Level Sensors An easily installed Water Level Sensor activates an audible alarm when the level of water in a container reaches 10% of its capacity As well as letting you know when to top up your water tank, the device helps guard against the danger of pumping air if the water supply runs dry - the surest way of causing expensive and inconvenient pump damage. Suitable for use with Car windscreen washer bottles and caravan, Motor Home or Boat Water tanks.