Water is needed by animals to drink and maintain body fluids, metabolize nutrients, and produce milk (which is nearly 87% water). Water is also used for crop production, cleaning the milking parlor, and in some cases for manure handling. Besides being an important input, water is also an output of dairy farms, which could have negative environmental and health impacts if the water mixed with manure or other waste streams are not managed properly. This is especially true if water containing pollutants reaches surface or groundwater streams potentially contaminating aquatic ecosystems and drinking water. It is important to identify potential water savings measures and to understand water quality issues for prevention and implementation of control strategies.

Water Use

Water inputs on dairy farms are classified as green or blue water based on source. Green water is the consumption of soil moisture due to evapotranspiration and blue water is the consumption of ground and surface water (1). Green water is part of the water cycle and thus, does not represent a depletion of resources. However, it is important to know green water consumption as it is part of total water use of the farm and is useful to prepare for variations in the natural water cycle due to changes in ecosystems and climate. In contrast, blue water has a limited supply. Regardless of the source, conservation strategies to limit use are important to integrate on all dairy farms.

Total water consumption on a dairy farm can vary significantly based on many factors including region and climatic conditions, diet composition, and management practices. A global study exploring the water footprint of dairy farms reported average green water use of 107 gallons/pound of energy corrected milk (ECM) in North America ranging from 66 to 115 gallons/pound ECM (2). Blue water consumption averaged 11 gallons/pound ECM ranging from 5 to 15 gallons/pound ECM.

Green water is mostly used for crop production and imported feed supplements. Blue water is primarily used for cows to drink, milking processes, and irrigation in regions where green water supply is not enough to support crop consumption. On average, a 1,500-pound lactating dairy cow can drink from 18 to 40 gallons per day depending on dry matter intake, milk production, and weekly mean temperature (3, 4). Non-lactating animals consume less water as they are not actively producing milk, but their daily water requirements are still 13 gallons for heifers younger than one year and 21 gallons for heifers older than one year (4).

Blue water used for irrigation can have a large impact on water supplies particularly in regions with water scarcity, such as the western United States, with alfalfa hay and corn silage among the most water-demanding crops (5). Blue water is also used to clean the milking parlor and the barn, especially when flush systems are used to collect manure, and for sand bedding recycling.

Water Quality

Livestock is one of the largest contributors to water quality impacts. Water lost from crop fields and farmstead areas can increase pathogens, nutrients, and organic matter in surface and ground water. Water containing nutrients can cause eutrophication, killing fish populations and affecting aquatic ecosystems. Contaminated groundwater with pathogens and nitrates can have serious health impacts for humans as groundwater is a major source of drinking water in the U.S.

Water discharged from a dairy farm which contains pollutants is known as grey water and can lead to environmental and health impacts if not properly managed. On average, nearly 9 gallons of grey water per pound of ECM (from 4 to 14 gallons/pound ECM) are produced from dairy farms in North America (2).

On the farmstead, grey water can be lost from outdoor housing areas, manure storage structures, manure processing areas, feed storages, and the milking parlor. It is a common practice that manure storages receive both manure and wastewater from the barn and milking parlor. These storages have engineering standards for design to ensure they are sized properly and limit losses to the environment. Farms commonly attempt to keep fresh water clean by avoiding physical contact with potential contaminates.

Land application of manure and fertilizers can contaminate surface water through runoff and can contaminate groundwater through leaching. The major issues from cropland runoff include discharge of nutrients, organic matter, pathogens, and increasing oxygen demand in water sources.

One of the first steps to avoid leaching and runoff problems from manure and fertilizers from land application is developing and then following nutrient management plans. These plans help farmers determine the best timing to land apply manure, optimal rates of application to limit losses, and help identify potential areas of concern. Conservation practices, such as using cover crops, crop rotations, buffer strips etc., can also help minimize losses of water quality contaminates from crop fields.

References

1. Murphy E., I.J.M de Boer, C.E. van Middelaar, N.M. Holde, L. Shalloo, T.P. Curran, and J. Upton. 2017. Water footprint of dairy farming in Ireland. Journal of Cleaner Production. 140:547-555. https://doi.org/10.1016/j.jclepro.2016.07.199
2. Sultana M.N, M.M. Uddin, B.G. Ridoutt, and K.J. Peters. 2014. Comparison of water use in global milk production for different typical farms. Agricultural Systems. 129:9-21. https://doi.org/10.1016/j.agsy.2014.05.002
3. National Research Council (NRC). 2001. Nutrient Requirements of Dairy Cattle, 7th Revised Edition, National Academy Press, Washington D.C. https://doi.org/10.17226/9825
4. Ridoutt B.G, S.R.O Williams, S. Baud, S. Fraval, and N. Marks. 2010. Short communication: The water footprint of dairy products: Case study involving skim milk powder. Journal of Dairy Science. 93:5114-5117. https://doi.org/10.3168/jds.2010-3546
5. International Dairy Federation (IDF). 2017. The IDF guide to water footprint methodology for the dairy sector. Bulletin of the International Dairy Federation 486/217. https://store.fil-idf.org/product/bulletin-idf-n-486-2017-idf-guide-water-footprint-methodology-dairy-sector/