The new urban drinking and wastewater chain: small, concentrated and sustainable

Climate change and the depletion of natural resources make it clear that we have to arrive at more sustainable solutions to keep the urban environment safe and habitable. The same applies to our urban water facilities. To do that job properly, it is important to understand the overall history and role of the three institutions in the current system in order to put the transition to “Small, concentrated and sustainable” in perspective.

Water authorities were the first institutions to get involved explicitly with water. The oldest of them go back centuries. They are responsible for keeping the country dry and establishing the best possible conditions to ensure that the scarce and fertile land in the delta regions is suitable for agriculture and industry.

The drinking water companies began supplying drinking water on a larger scale ‘only’ at the beginning of the last century. At first, they were generally municipal, provincial or private companies but they have now been structured as ten public companies with a legally determined and clearly defined task. They grew rapidly during the period after the Second World War until the 1980s in line with the general development of the country.

The responsibilities of the municipalities in the water domain also began to pick up momentum during the same time. Their tasks were focused primarily on preventing disruption caused by rainwater, and they were soon combined with the collection and disposal of waste water in dedicated and general drains. In turn, this resulted in a new task for the water authorities in the early 1970s: the treatment of waste water before it was allowed to return to the river or water system.

Each institution is now still responsible for one link in the chain, the common thread being public health and ‘urban comfort’. The quality and performance of the overall system are unique in the world, and Dutch ‘water science’ is a focus of admiration, and sometimes envy.

The drinking-water and wastewater chains must be more sustainable to safeguard the availability of adequate supplies of clean water. Currently, all the institutions look primarily at measures in their own domains. This sometimes leads to solutions that are effective in the individual domains but that fail to contribute to, or may even be negative for, other domains. Optimisation in this respect requires the establishment of an overall focus on retrieving basic materials from wastewater flows. An important result of this in technical terms is that wastewater flows should as concentrated and as constant in composition and volume as possible: small, concentrated and therefore very sustainable to treat! This allows for the application of the most efficient and energy-neutral treatment/recovery process, anaerobic treatment (i.e. without oxygen).

For the various water institutions, this means a paradigm shift. The sustainability objective transcends institutional boundaries and it is not covered by the current statutory obligations. The point is to keep as much water as possible out of the wastewater flows and to maximise the amount of organic matter in those flows. This makes it more important, for example, to save on the total volume of water used in a home or industry (smaller and more concentrated) than to replace part of the drinking-water flow with rainwater.

Most ‘dilution’ of the wastewater flow now takes place in the municipal drains system. Even in a separate system, rainwater and other water flows have a major effect on volumes and therefore on dilution. Smaller sewage pipes (100-150 mmm instead of the usual 300 mm) prevent misconnections with rainwater and therefore concentrate the flow. Collection systems with smaller and shorter pipes take up less space in the ground and, not unimportantly, they are 50% cheaper than conventional dirty-water sewers.

In time, these interventions, in combination with drinking water savings, will result in the desired small, concentrated wastewater flow. It will take a number of decades to adapt sewers and achieve water savings. It is even possible that additional nutrients will be needed to obtain the optimal concentration of organic matter, for example by also adding kitchen waste to waste water; or the dog faeces we now throw into the rubbish bin in bags.

In short, this means making the urban drinking-water and wastewater chain sustainable on the basis of the principle of concentrating and reducing the wastewater flow. The central issue is always: “What does measure XX contribute to the reduction of wastewater flows, or to increasing the concentration of organic matter?”