Water has many exotic physical properties: surface tension, transparency in green and blue wavelengths (allows photosynthesis), protection from wavelengths shorter than UV light (high biodiversity). Surface water however looses lots of biodivserty (76% in freshwater, 39% in seawater).

The physiological water cycle in humans consist of 5 litres of blood that transport sugars, amino acids and fatty assets as well as “waste treatment plant” in the kidneys. Similarly, we can consider the water cycle on Earth. Water equalises global temperature, it is a greenhouse gas (around 33°C compared to without water).

Water pollution influences water quality tremendously. Point sources such as sewers, industrial effluents and diffuse sources such as pesticide treatment require different strategies.

Self-purification of water is a process where bacteria (spherotilus and protozoa) are increased through sewage, however once they use up the organic matter they decrease. Other side products are ammonium and nitrate which are then used by algae to grow. Dense population requires unpolluted areas in a river to work. To improve river quality sewage treatment plants have been built to reproduce self-purification in a controlled environment and only let cleaned water is released. However, the process is faster and sludge of bacteria need to be gathered and treated separately. This approach however only works for point sources where we can collect the sewage before it mixes with clean water.

Chemical pollution (dispersed) needs to be tackled differently. Often chemicals are regulated in order to keep pollution levels low. Especially, micro-pollutants are dangerous (antibiotics from hospitals and farms could contribute to the evolution of multi-resistant pathogens; carcinogenic compounds should not enter water cycle).

Risks can be mitigated by front-of-pipe, process, and end-of-pipe solutions. For instance an additional step in sewage treatment plants to remove micro-pollutants before the traditional process is an upcoming technology.

Agriculture

Improved water nutrient efficiency allowed to handle the increased food consumption  of the growing population. A side effect is that nitrogen (7-fold increase for doubling of output) and phosphorus have been increased. Algae grow in the ocean where the rivers deliver the fertilizer and those algae take out oxygen effectively killing the ocean in the respective areas (so-called dead zones).

To reduce those factors, improve cultivars, optimize irrigation systems, minimize crop loss and stop food waste.

Industry

Zero-emission/low-emission is newly formulated goal of many industries. Zero-emission gives a competitive advantage at it means that less regulations apply.

For example in the copper industry 100m3 water are used to treat 100tons of ore. Ore is ground, floated and moves from 1% to 30% copper. At that rate you can transport it and refine it elsewhere. The waste water generated is highly toxic and needs sewage water treatment. The ore produces 99 tons of tailings per ton of copper. In a second step copper is smelted and you get 70% to 99.5% pure copper, and the waste is a slag of water and sulphuric acid. In a last step refining takes place to reach 99.99% coper with a waste water filled with precious metals.

The process can be optimized to reduce water consumption and waste production and treatment.

Urban systems

Zürich has 1000km of urban sewers, 3100km of private pipes and around 200 pumping stations, retention basins and more. The infrastructure is worth about 200 billion CHF.

In most parts of the world sanitation tanks collect waste, it gets collected, (hopefully) treated, and then disposed.

Those different context require different approaches to solve the problem. Income and rainfall are important factors in the design of the urban water system. Drinking water and sanitation are difficult to provide in low-income, low rainfall regions.

Water quality impacts the development of children and sanitation and hygiene as well as water treatment are needed to improve their chances to develop normally.To reach those goals measures need to be simple, work for everyone and be cheap. They must also be culturally sensitive in order to be successful.