Quality of waste water
Waste water (from homes and businesses) contains a wide range of polluting substances. To guarantee a good quality of water, purification is necessary.
The drainage and treatment of waste water
The collection and transport of waste water from households to sewage treatment plants happens through sewage systems (the public sewers). The Netherlands has more than 90,000 kilometres of sewer lines. This falls under the responsibility of the municipal governments.
At the sewage treatment plants, the foul water is treated and purified. This is the responsibility of the district water boards. The Netherlands has 25 district water boards that together manage 350 sewage treatment plants.
A large part of the industrial waste water comes to the sewage treatment plants via the sewer system as well. This commercial waste water is often pre-purified by the discharging companies themselves.
There are exceptions to this: a small proportion of private citizens purify their waste water themselves because it is not cost-effective to lay a sewer line in the area where they live. This could be because they live way out in the country.
Responsibility of citizens and companies
The waste-water system cannot handle everything, despite the efforts of municipalities and district water boards. Private citizens and companies bear their own responsibility to keep environmental risks at an acceptable level. For households this means giving some thought to what can and what cannot be taken away by the sewer. Oil, deep-frying oil, wet wipes, kitty litter, paint waste, food waste, medicines or other chemicals should not be put into the sewer. They can cause stoppages or hinder purification.
Companies should make their water as clean as possible before releasing it into the sewer. They should also take measures to pollute water as little as possible. The rules for this are recorded in the permit of the company or in general regulations.
Separate drainage of rainwater
In addition to waste water, a substantial amount of rainwater also flows into the sewer. This is actually a waste of good water. Rainwater is (relatively) clean water, so transporting it to and treating it at sewage treatment plants is senseless. For this reason, rainwater in newly built districts is not drained into the sewer. Instead, companies and private citizens are connected to a system that drains the rainwater directly into lakes and drainage ditches or ground water. Municipalities can also drain the water via a separate sewage system (rainfall system). This practice is called disconnecting the rainwater.
Disconnecting rainwater means that, during heavy rainfall, the sewers have a smaller chance of overflowing and thus causing a part of the sewer water to flow into lakes and canals or flood the streets. The sewage treatment plants also operate more efficiently when the waste-water is no longer diluted by rainwater.