Water pollution is a global challenge that has increased in both developed and developing countries, undermining economic growth as well as the physical and environmental health of billions of people.Agriculture is the single-largest cause of non-point-source pollution to surface water and groundwater, accounting for 70% of total water usage globally. Increased soil erosion, salinity, and sediment loads in water are frequently associated with agricultural intensification, as is the excessive use (or abuse) of agricultural inputs (e.g. fertilizers) to boost production. Agriculture-related pollution can pollute water, food, fodder, farms, the natural environment, and the atmosphere. Pesticides and fertilizers used in agriculture, as well as organic animal wastes, antibiotics, silage effluents, and processing wastes from plantation crops, can pollute both groundwater and surface water. Pollution from large-scale industrial agriculture (including livestock and fisheries) is classified as point-source pollution, whereas pollution from small-scale family farms is classified as non-point-source pollution.

Farmers are increasingly turning to non-conventional water sources of poor quality, such as wastewater, as demand for agricultural goods rises. Because of its high nutritional content, domestic and municipal wastewater is an appealing choice, especially when traditional water supplies are few or unavailable .The improper use of non-conventional water sources in agriculture, particularly wastewater, can result in the accumulation of microbiological and chemical pollutants in crops, livestock products, soil and water resources, and, ultimately, severe health consequences for exposed food consumers and farm workers, as well as exacerbate antimicrobial resistance. However, if properly cleaned and utilized, wastewater may be a useful source of both water and nutrients, helping to enhance food security and livelihoods.

The potential of groundwater to operate as a stable water supply for irrigation, providing water on demand while being mostly unaffected by seasonal surface hydrological change, explains the rising relevance of groundwater for agriculture. In many areas, the growth of groundwater irrigation has led to the usage of groundwater beyond natural recharge. Continued abstraction lowers water tables, which raises pumping costs and may lead to a "race to the bottom" among producers. In certain locations, intensive groundwater withdrawals for agriculture have resulted in depleted streams, rivers, and lakes, as well as the potentially permanent salinization of aquifers in coastal areas, affecting all surface water users, including farmers, and harming ecosystems. Land subsidence is also a result of intensive pumping in some locations, causing significant damage to infrastructure in both urban and rural areas and reducing the ability of aquifers to retain water for future needs.

Pollutants that result from farming and ranching include sediment, nutrients, pathogens, pesticides, metals, and salts. Impacts from agricultural activities on surface water and ground water can be minimized by using management practices that are adapted to local conditions.

Reference

https://wateractiondecade.org/2017/12/09/water-pollution-from-and-to-agriculture/