Currently, sources from which renewable energy could be generated are being sought worldwide. One of these sources could be wastewater. This article shows how heat can be recovered from wastewater, using a small wastewater treatment plant in Świętokrzyskie voivodeship as an example. It analyses the temperature of wastewater in the reactor, in the sewage system and the ambient temperature for each month. The principle of heat pump operation was presented. Then, the amount of heat energy that can be recovered from wastewater was calculated for each month.