A method is provided for extracting heat from a hot liquid containing scaling material whose solubility is proportional to the temperature of the liquid. The method includes providing a pond containing a liquid, and locating in said pond a vertical tube having an upper end that is substantially closed, and an open lower end immersed in the liquid in the pond and spaced from the bottom thereof for establishing a trapped region above a column of liquid in the the tube. Hot liquid is supplied to the trapped region, and the pond and the tube are constructed and arranged so that the liquid in the pond and the liquid in the column are in substantial hydrostatic equilibrium. As a consequence, the trapped region is maintained at a pressure such that some of the liquid supplied to said trapped region flashes into a vapor thereby concentrating the liquid in the column. Finally, the open lower end of the tube effects the passage to the bottom of the pond of scaling material that precipitates as a consequence of the concentration of liquid below the trapped region.