The invention relates to a process for the purification of water and/or dewatering of sludges and/or sediments, to the use of a combination of a phyllosilicate and a surface-treated calcium carbonate for water purification and/or dewatering of sludges and/or sediments, as well as to the use of a combination of a phyllosilicate and a surface-treated calcium carbonate for reducing the amount of polymeric flocculation aids in water and/or sludges and/or sediments and to a composite material comprising at least one surface-treated calcium carbonate, at least one phyllosilicate and impurities originated from different sources obtainable by said process.