Water pollution is a global challenge undermining global growth and threatening the world’s freshwater reserves. Agriculture is one of the primary causes for water pollution.
Hundreds of millions of people are at risk of being affected by coming in to contact with these polluted waters .
Water Pollution Facts
Water is essential to our very existence, especially the freshwater reserves. However, it is also quite vulnerable to pollution as its a universal solvent i.e. water can dissolve more substances than any other liquid.
As a result, toxic substances and waste coming from industries, agriculture and human use can dissolve readily, causing water pollution.
Natural calamities like floods, earthquakes, surface run-offs due to rains and winds, oil spills in oceans are also other sources of water contamination .
Below diagram highlights the freshwater withdrawals %.
Sector-Wise Freshwater Withdrawals %
Source: UN Millennium Development Goals Report -2015
UNESCO claims that around 80% of the world’s wastewater is discharged back in the environment without adequate treatment, and since agriculture withdraws the maximum freshwater, it’s also the biggest source of water pollution [6,17].
The 3 biggest sources of water pollution related to agriculture being animal waste, aquaculture production and fertilizers used in agricultural fields.
Causes of Water Pollution
There are many sources of water pollution; however, we’ll be only focussing on agricultural-related pollution sources.
Livestock farming contributes to water pollution in 2 significant ways.
1: Most of the water used for livestock drinking and servicing returns to the environment in the form of liquid manure, slurry and wastewater.
The wastewater contains a high amount of total organic carbon (TOC) originating from the use of pesticides, growth hormones, drug residue, antibiotics, blood and animal waste .
2: Surface runoff caused by rain or wind carry all the sediments (soil erosion) along with pollutants (animal manure, chemical fertilizers) from agricultural farms.
Breeding fishes for food in a natural environment like oceans and rivers is a risky business. Many types of aquaculture production require chemical treatments for a successful harvest .
Quite often, the wastewater from these farms is released directly in the adjacent water bodies which can cause significant water pollution.
Furthermore, fish farms generate a substantial mount of pollutants such as fish excretement, uneaten fish food and other organic wastes
Pesticide use and on-farm disease can also affect local species .
Since more than 50% of the world’s seafood now comes from aquaculture, the scale of pollution caused due to aquaculture related practices is an important cause of concern .
For e.g., In Scotland, the 3rd biggest producer of salmon fish, the discharge of untreated organic waste from salmon production is equivalent to 75 per cent of the pollution discharged by the human population.
Every year 25 billion tonnes of sediments are transported from agricultural fields into the waterways . The topsoil is loosened when land is converted to agricultural lands.
Soil can also be loosened due to the hoof action of animals or due to overgrazing vegetation . When that happens, the soil loses its water holding capacity and is eventually washed away into water bodies.
Ground Water Pollution
Plants need nutrients for growth and survival. Due to increased demand for agricultural products and declining fertility of the soil, the farmlands are fed with tonnes of synthetic fertilizers.
The 2 most essential nutrients used for boosting the productivity of the land are Nitrogen and Phosphorous.
However, over-fertilization is a bigger problem than under fertilization. When plants cannot absorb all the nutrients from the soil, the nutrients along with other chemical pollutants end up percolating down and polluting the groundwater reserves .
Several studies have pointed out that Nitrate is the biggest chemical contaminant of groundwater reserves 
Consequences of Water Pollution
Various pollutants coming from farmed lands and aquaculture production are not only polluting the oceans but also our freshwater reserves which are scarce.
The polluted water is no longer fit for human consumption, and, it can be responsible for a range of other issues.
Dead zones occur when freshwater carrying lots of nutrients, Nitrogen (N) and Phosphorous (P) meets the sea. Animal manure and synthetic fertilizers used in farms are abundant in these nutrients .
These nutrients along with other chemical pollutants stimulate the growth of algae, aquatic plants and bacteria that can dissolve oxygen in water, a process also referred to as Eutrophication .
It is estimated that Pig slurry has 150 times more nutrients than domestic sewage .In terms of aquaculture production, for every tonne of fish produced, there is 42-66 kg of Nitrogen (N) and 7-10 kg of phosphorous (P) waste produced  .
As a result of N and P pollution, more than 400 dead zones have been identified globally in the oceans and rivers . These dead zones no longer support any ocean life and are spread across 250,000 sq. km, an area bigger than the size of Japan or Germany. [1, 10]
Once the groundwater reserves are polluted with agricultural related pollutants, the aquifer may be unusable for decades, sometimes even thousands of years .
Not only that, but many times groundwater contamination can also spread far from the original polluting source as it seeps into streams, lakes, and oceans. 
This is bad news as groundwater reserves provide drinking water to at least half of the world’s population as well as account for almost half of the water used for irrigation .
As per reports, 20% of the underground water reserves are already considered over-exploited or polluted.
It is anticipated that the number of dead zones in freshwater bodies and oceans caused due to livestock farming, industrial waste and aquaculture production would continue to rise until 2030. The number of lakes with harmful algal blooms will increase by at least 20% until 2050 .
With the world’s food production expected to double by 2050, there will be a corresponding increase in fertilizer production and that necessarily means the groundwater reserves might further shrink due to agricultural pollution [5,7]
Already 50% of the world’s population is living under water-stressed regions and that is expected to increase even more by 2050 . Water pollution caused due to the above reasons would play a big part in aggravating the situation.
Impact of Soil Erosion
Apart from the economic costs, the erosion process caused due to livestock farming blocks waterways and increases the possibilities of floods . The sediments increase water turbidity and that means less sunlight for plant and algae growth.
It also raises the surface temperature, affects respiration and digestion of aquatics organisms . Streambeds and coral reefs, which are nesting sites and food sources of fishes are blanketed with fine sediments .
Several of the deadly known bacteria’s and pathogens that are resistant to antibiotics and capable of infecting humans are present in abundance in animal manure and in the wastewater coming from slaughterhouses. 
When these superbugs are washed away into water bodies, they are known to develop further and reproduce, exchanging genetic information. In doing so, they enlarge a large pool of bacteria that were once resistant to powerful antibiotics .
The bottom line – Water pollution-related diseases claims more than 2 million lives annually due to unsafe drinking water, poor sanitation and natural disasters like floods, earthquakes etc. .
Are our food choices also indirectly responsible for the high mortality rates and shrinking freshwater reserves?