Abstract: Apparatus for obtaining pure water from crude water includes an evaporator arrangement (10) that has a first circuit (101) for cirulating crude water, a second circuit (102) for circulating liquid coolant, and membrane elements for separating the circulating crude water form the circulating liquid coolant and for obtaining pure water from the crude water by a membrane distillation process. Connected to the first circuit (101) is one side (111) of a heat exchanger (11) for raising the evaporator arrangement (10). The apparatus also includes a heat pump (12) for lowering the temperature of the liquid collant prior to said coolant entering the evaporator arrangement (10). The high-temperature side (121) of the heat pump is connected to the input side (1021) of the second circuit (102) via the remaining side (112) of heat exchanger (11) and a cooling device (13). The low temperature side (122) of the heat pump is connected to the output side (1022) of the second circuit (102).