Water use by New Zealand dairy farms, 1997-2000

New Zealand dairy farms use water for pasture irrigation, stock drinking water and dairy shed washing. Stock drinking water and dairy shed wash water are readily determined on a "per head" basis, but there is limited information on the amount of water used for pasture irrigation. In this work, a method for estimating the annual water use for irrigation of New Zealand dairy pasture in 13 regions has been developed using data on regional water allocation and regional soil moisture data. The estimate of water used for irrigation was validated by a comparison with monitored irrigation on four Canterbury farms. Total annual water use by New Zealand dairy farms in 13 regions was estimated over the 4-year period from 1997/98 to 2000/01 and averaged 10 17 million cubic metres per year. On average, 892 million cubic metres (88%) of all water used by New Zealand dairy farms was used for pasture irrigation and the remaining 125 million cubic metres (12%) was used for stock purposes. On average, 62% of all water use occurs in the Canterbury region. Estimated total water use remained fairly constant for the first 2 years of the analysis. It then dropped significantly in 1999/2000 and rose significantly in 2000/01. Since irrigation water use is approximately seven times greater than water use for stock, and approximately 75% of irrigated pasture area occurs in the Canterbury region, it follows that soil moisture in the Canterbury region has a dominant effect on the annual water use on New Zealand dairy farms. Total annual water use on New Zealand dairy farms was apportioned between surface and groundwater sources. On average, approximately 72% of the 1017 million cubic metre per year total water use came from surface water sources. The remaining 28% came from groundwater sources.