Water effluent from New Zealand dairy farms from 1997 to 2000

New Zealand dairy farms make a significant contribution to the country's environmental pollution. In particular, they produce large quantities of effluent water which contaminate the ground and surface water. An important step towards assessing the extent of contamination is to quantify the amount of water effluent produced annually from dairy farms. This is the focus of this paper. The annual volume of water effluent from New Zealand dairy farms from 1997 to 2000 is determined from a water balance for 13 regions covering the country. Two commonmethods for disposal of farm dairy effluent are considered, namely irrigation of effluent directly onto the land and pond storage followed by a combination of irrigation and discharge to surface water. Finally, the annual volume of effluent discharged to ground and surface water is estimated over the 4‐year period for each of the 13 regions. The analysis finds that New Zealand dairy farms produced an annual average of approximately 960 million cubic metres of effluent water, of which an average of 59% went to surface water. The estimate of effluent volume is very imprecise, relying upon constant countrywide rates for drainage through the soil and for seepage from effluent ponds. However, in the absence of more accurate data, it was judged better to provide a rough estimate rather than no estimate at all. The sensitivity of the analysis to variations in the assumed parameters is examined.