A gutter or drain water level sensor arrangement

A gutter water level sensor 10 comprises a main body 6a,6b having an outer wall which defines a chamber 7. First 1a and a second 1b electrodes are located within the chamber and separated from each other. The electrodes are substantially sheltered from water falling onto the outer wall of the main body. Water can rise up into the chamber 7 though an inlet at its lower end to provide a conduction path between the electrodes. The inlet may be covered with a grille or mesh (8, fig.3) which prevents detritus from entering the chamber. Air vents 9 allow air to enter or leave the chamber 7, but they are angled to reduce the risk of rainwater entering. The electrodes may be insulated from each other by a block 4 of hydrophobic material. A monitoring system connected to one or more such sensors issues an alarm based on a comparison of the electrical resistance of the sensor with a predetermined threshold.