The constantly growing water deficit in agriculture contributes to the fact that digestate, which is a by-product of biogas production, begins to be treated not only as an alternative fertilizer but as a potential source of water. Digestate is a rich source of nutrients and water. However, European Nitrates Directive (91/676/EEC) could become a significant obstacle for direct application of the digestate by means of land-spreading, due to high availability of the nutrients in the digestate. Storage is also difficult, as state-of-the-art biogas plant has a substantial land requirement for the storage of digestate. The use of hydrothermal carbonization process (HTC) can enhance the mechanical dewatering of digestate and make it less energy intensive. On top of that, liquid by-products of hydrothermal carbonization can be used to enhance the biogas production, due to their relatively high content of organic compounds while recovered water may be used in agriculture. This paper presents the results of the use of various polymer membranes for purification of water from the HTC effluent, after hydrothermal carbonization of an agricultural digestate.