The quality of dirty water arising on 20 dairy farms in England and Wales was investigated. Farms were selected where existing pumped dirty irrigation systems allowed for appropriate sampling. Each farm was visited on three occasions during the year, in March, June and September, to sample dirty water. Considerable variations were found in total solids (TS) with concentrations ranging from 0.08% to 4.64%. Marked seasonal variations were observed with the highest concentrations in June and the lowest in March. The biochemical characteristics of dirty water showed fairly good correlations between the following parameters and TS: 5-day Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Kjeldahl nitrogen, potassium and phosphate. No corresponding correlation was found for ammoniacal nitrogen concentrations. These findings indicated that effective biological treatment for dirty water was feasible.