Groundwater can be considered as a non-polluting renewable energy source. It can be used as a fluid in the industrial, commercial, and residential building heating and air-conditioning systems. Usually, the water table is deep enough, so the atmospheric conditions have a negligible influence on the water temperature. For that reason, the annual variation in the temperature is minor, therefore, the groundwater can also be considered a reliable energy source. This paper presents some aspects of the heat pump wells design and addresses specific problems that can occur during their exploitation. The heat pump system consists of two types of wells: exploitation and drainage well. It is shown that the distance between the two is a crucial parameter that affects the whole system efficiency. An example of wells design for a production hall heat pump is given. The wells are constructed is in the northern part of Croatia. The geological and hydrogeological conditions at the site are highly favourable regarding the water temperature and soil hydraulic conductivity. Because of the insufficient distance between the wells, the temperature in exploitation well rose, which reduced the heating system efficiency.