Investigation into the occurrence of aquatic invertebrates throughout drinking water purification plants

World-wide, invertebrates are found in most drinking water networks; however, limited data and information are available on the occurrence of invertebrates throughout the purification process. During this investigation, temporal and spatial variations in the invertebrate composition occurring throughout a conventional Drinking Water Purification Plant (DWPP) and the abiotic drivers responsible for their occurrence were investigated. Samples destined for invertebrate and water quality analyses were collected and multivariate statistical analysis was performed on the data obtained. Copepoda, Rotatoria, Cladocera, Ostracoda and Diptera were the dominant groups found in the source water and occurred throughout the purification process. A higher total biomass occurred throughout the purification process, in particular after sedimentation and filtration, compared with the total biomass entering the DWPP. The water quality variables measured were within the optimum ranges of invertebrates. The present study proved the theory that purification plants are an important source of invertebrates occurring in the drinking water distribution network. Strategies should be implemented to improve coagulation (by using coagulants/flocculants to increase the pH above 10.5), flocculation, sedimentation (by removing sludge and algae) and filtration (by optimizing filter bed maintenance) and general filter house ‘housekeeping’.