Insulated water tank for use with the Ratek range of Thermoregulators. Includes plumbing fittings enabling a supply of temperature controlled water to be circulated to an external sealed system. The inner tank is fabricated from 304 grade polished stainless steel, and the outer case from a chemical resistant plastic. 25mm of insulation is used between the tank and case to minimise heat loss, allowing for stable temperature control.