Abstract: Cooling water is supplied to a load, e.g. a thermal-power station, from a source of water such as a lake or stream susceptible to changes in level. The system comprises a first pump drawing water from the source, a filter arrangement downstream of the first pump, a duct downstream of the filter arrangement and a second pump connected between the duct and the input side of the load. The downstream side of the load, from which the warm water emerges, is passed through a second duct and then preferably through a warm-water level control arrangement before being disposed in a sink or other basin. A connection between the discharge duct and the feed duct is permanently maintained and allows water to flow from the feed duct to the discharge duct or vice versa in dependence upon the relative quantities of liquid displaced by the pump. As a result, the water fed through the second pump can have its temperature adjusted by mixing with warm water automatically.