This sub-class includes: •operation of sewer systems and/or sewer treatment facilities •treatment of wastewater (e.g., human and/or industrial wastewater, water from swimming pools) by means of physical, chemical and/or biological processes like dilution, screening, filtering, sedimentation, etc. •maintenance and/or cleaning of sewers and/or drains, including sewer rodding •operation of wastewater treatment facilities, for the reuse of e.g., agricultural, industrial, road cleaning or collected rain water, or for artificial recharge or augmentation of groundwater bodies •freeze drying of sewage sludge by wastewater treatment plants •emptying and/or cleaning of cesspools and/or septic tanks, sinks and/or pits from sewage •servicing of chemical toilets