Water pollution is mainly caused by chemically treated and raw sewage, waste from domestic farm animals and industrial liquid waste. Other water pollutants include pesticides, nitrates, phosphates, metals such as copper, zinc, cadmium and mercury, and chemical wastes including complex organic compounds. In the sea, the majority of the pollution is from rivers and coastal discharge, some is from rainfall and some is as a result of illegal dumping from ships and boats. The proportions will vary according to the location.
Many coastal countries dump their sewage into the sea. Many rivers, particularly in the developing world, have a problem with sewage. Some of this sewage is untreated raw sewage and some is treated with chemicals.
Many boats pump untreated sewage directly into the water. Some have toilets that pulverise and pump the waste out. There are no visible solids but the nutrient and bacteria content remain the same and so does the health problem. The risk from consuming contaminated seafood is higher in areas where boats are moored and occupied for extended periods.
The effects of sewage pollution include deoxygenation and turbidity; resulting in suffocation, disease and death of fish and other marine organisms; damage to ecosystems; and build-up of toxic metals and chemicals in the food chain. As a result of sewage, the water in many countries is not safe for bathing or fishing. Sewage degrades the environment, endangers health, and destroys fisheries.
One-fifth of the global population is obliged to drink unsafe water, most of which causes diseases such as malaria, cholera and schistosomiasis. Three million people die annually from diarrhoeal diseases caused by water polluted with microorganisms – viruses, bacteria and protozoan parasites. The majority of the victims are children. Many Third World governments with huge debts to pay off, do not introduce water sanitation facilities because of cost.
Sewage has potential value as compost, or as an energy source. Some countries are treating their sewage, extracting the energy/compost component and re-using some of the water in ways that do not cause a health risk. However, most countries do not come up with any better solution than to build longer pipes to take the pollution further out to sea.
Nitrate is by far the most common chemical contaminant found in groundwater. Most of it is from fertilisers, added to the soil to grow crops. Groundwater may be so contaminated that it must be treated to reduce nitrate levels. High amounts of nitrates are leached into drinking water as a direct result of the fertilising of monocultures in agriculture. This can lead to ‘Blue-Baby Syndrome’ and contribute to the death of infants.
Farm fertilisers also contain phosphates which add to the groundwater and river pollution. Rain flushes fertilisers and pollutants into the rivers. In hot conditions and in stagnant or slow moving water-bodies polluted with fertilisers, sewage and animal waste – algae flourish. Some of these algae are able to survive in salt and fresh water, and some varieties of algae can produce toxins.
The algae are most toxic when they die and decompose. Algal blooms suffocate and kill fish and other marine organisms, cause toxic build-up and poisoning of shellfish, clog up harbours and make beaches unpleasant. It is unsafe for human beings or animals to drink this water, and water containing toxic algae should not be used for irrigation. Chlorine may be added to water supplies to wipe out toxins from an algal outbreak. Authorities usually ban fishing, swimming and boating. Algae can cause eye and skin irritation, and liver damage if ingested. The toxins may cause gastrointestinal, neurological and paralytic illnesses or even death when contaminated fish are consumed.
Many chemical pollutants are so new in the environment, we do not know how dangerous they are. They are tested in a laboratory but not on an entire marine ecosystem. Metals such as mercury and slowly degrading chemicals threaten inland and coastal waters. In the USA over 800 contaminants were identified in the waters and sediment of the Great Lakes. These toxic materials harm wildlife, and in the food chain they contaminate fish and shellfish that we consume.
Dioxins are very toxic. They can cause genetic changes in marine life, and are suspected of causing cancer in human beings. The industrial compounds known as PCBs (polychlorinated biphenyls) can cause reproductive problems in some animals, and accumulate as they pass along the food chain.
Salinity levels on land and in rivers are increasing, due to the ongoing farming practice of substituting native vegetation with shallow-rooted crops. Rising groundwater levels bring salt to the surface and rain washes it into the rivers. The salt affects ground level vegetation, wetlands and other water bodies. The consequences of salinity are costly, both economically and ecologically. Farmland, buildings, infrastructure and habitats are destroyed by salt.
Modern societies produce vast amounts of grey water, i.e. waste water which is not contaminated with toilet water. Some of this can be recycled in gardens. It should be noted that health departments are cautious about re-using shower and bath water, which can be contaminated by body wastes and could lead to infection. Kitchen water often contains grease and highly toxic detergents that are damaging to the soil. In addition, sewer systems are often designed to be flushed with grey water.
What this means is that using grey water is not a sustainable option at this time for many situations unless careful precautions are taken and other changes in lifestyle are made. The laundry does offer some scope to bucket rinsing water and use it on the domestic garden.
The future of substantial grey water recycling may actually be in small local community plants. Revised building regulations should ensure future homes are built with more advanced and sustainable plumbing systems.
What you can do
If your local government is not managing your waste satisfactorily, install a wastewater treatment system in your home such as a composting toilet and disconnect from the sewer. Check with your health department to make sure your planned system complies with local health regulations. Re use some of the grey water from the laundry. If you own a recreational boat ensure it is fitted with an environmentally appropriate toilet facility or treatment system. Press your ports into operating a sewage receival station.