Towards Sustainable Dairy Water Management

Evidence and innovations for better on-farm solutions.

Dairy Soiled Water (DSW) is an effluent produced on dairy farms though the washing of parlours, holding yards, and milking facilities. DSW consists of 86% wash water, 10% excreta, and 4% teat washings. As dairy production intensifies globally, excessive freshwater use and DSW run-off have become increasingly recognised environmental concerns. Countries such as Ireland, Italy, and New Zealand are facing similar challenges, where intensive dairy activity places pressure on local water systems. With its high nutrient and organic load, DSW can threaten rivers and groundwater when not effectively managed.

On Irish dairy farms, a survey of 60 farms reported that around 9,800 L of DSW are produced per cow each year, containing 587 mg N L^-1 and 80 mg P L^-1, highlighting the significant nutrient load associated with this effluent ¹. Numerous studies have highlighted the risks associated with nutrient management from farm systems ^{2, 3}. Studies also suggest that cleaning parlours, yards, and milking facilities can require up to 13-30 L of water per cow per day, highlighting the large volume of fresh water required ⁴. These pressures underline the need for effective on-farm treatment systems. Constructed Wetlands (CW) are a Nature-based Solution (NbS) that can substantially reduce organic matter and nitrogen content in DSW, but long-term phosphorus removal is often only moderate (around 40-60%) as CW media become saturated ⁵. Hybrid systems that combine CWs with upstream phosphorus removal processes, such as chemical coagulation, have demonstrated much higher overall nutrient removal and offer a promising option for farms with high DSW loads ⁶.

These insights demonstrate that improved DSW treatment is essential to safeguard resources and reduce freshwater needs. By enabling the reuse of treated water, hybrid systems can help close the loop and support circular on-farm practices. Encouraging wider adoption though policy, guidance and on-farm trials will be key to mainstream these solutions.

1. Minogue, D., French, P., Bolger, T. & Murphy, P. N. C. Characterisation of dairy soiled water in a survey of 60 Irish dairy farms. Irish Journal of Agricultural and Food Research 54, 1–16 (2015).
2. Fasciani, C. Italy: Climate change boosts water pollution by intensive dairy farms. Water News Europe (2023).
3. McDowell, R. W. et al. High flows contributed a large part of annual contaminant yields in New Zealand’s rivers. Commun Earth Environ 6, (2025).
4. VanderZaag, A. et al. Water use dynamics with conventional and automated milking systems on a dairy farm. J Dairy Sci 108, 6025–6033 (2025).
5. Healy, M. G. & O’ Flynn, C. J. The performance of constructed wetlands treating primary, secondary and dairy soiled water in Ireland (a review). J Environ Manage 92, 2348–2354 (2011).
6. Mohamed, A. Y. A. et al. A novel hybrid coagulation-constructed wetland system for the treatment of dairy wastewater. Science of the Total Environment 847, (2022).