For an efficient and safe washing of insulators, the water must have a minimum of 2540 ohm-cm or 100 ohm-in resistivity or a maximum of 400 micro-siemens conductivity. An additional note to this is that resistivity of water decreases as water temperature increases. Hence, it is important that the resistivity/conductivity of water be measured constantly. Normally, washer packages include “Constant resistivity monitors”, which notify the operator if water conductivity rises above a pre-set level. These monitors can be installed to automatically turn off the washer is this limit is reached. Portable meters are also available and can test the resistivity or conductivity of the water before filling up the tank.