The second core activity is water quality management. After all, it isn't a question of just getting the right amount of water in the right place at the right time, but also that the water has the right quality; in other words, water quality that matches the intended use. For example, water for swimming must satisfy heavier requirements than water to be used for spraying crops. Similarly, water that ends up in the countryside, or water for agricultural use, must be of good quality. A basic principle of the District Water Board Veluwe is that all the waste water is returned to nature after being treated! Prevention is better than cure, so industry and agriculture have to satisfy many conditions to qualify for a permit allowing them to discharge into the sewer.
Every process involving water, including those in your own home, produces contaminated waste water. Fortunately, water has self-cleaning properties, but a large number of waste products such as heavy metals and pesticides do not decompose. If no action were taken, much of the surface water would become polluted and totally unusable: not as drinking water for livestock, not for spraying crops, not for use in industrial processes, and therefore also not for swimming in!
Most of the contaminated water is transported through sewers to water purification plants. These installations treat the water from residential areas, industry, and various recreational projects. The means used include bacteria that eat up waste products thus removing a large proportion of the phosphates and nitrogen compounds. The treated water is then released back into the surface water.
In many urban areas, household waste water and rain water are carried away through a system of sewers. In cases of heavy rainfall, the excess water in the sewers - the mixture of waste water and rain water - is sometimes discharged into the surface water. This untreated sewage then flows into natural streams, ponds, canals, pools, or ditches, with detrimental consequences for the plants and animals that live there. Fortunately, the number of sewer overflows has been reduced by discharging rain water straight into the surface water instead of into the sewer. In urban areas, more and more rainwater pipes on buildings are being disconnected from the sewer. The rainwater can then soak directly into the ground, and this also counters the drying out of the soil.
