Sustainable Urban Water Systems?

Water availability has always been the key factor for the development of human society. While in many countries this is plainly evident, those of us who – like me – live in a water-rich country, tend to forget about it. But even in my home country Switzerland – also known as Europe’s water tower – 2018 was a drought year.

Its famous glaciers, which currently still provide a constant water flow in the rivers throughout the summer months, keep melting away [1]. They are suspected to be completely gone by the end of the 21st century.

There are currently five main strategies for dealing with water-scarcity:

  1. Slowing down runoff and storing water, e.g., during the rainy season for later use in the dry season. The ancient “Wevas” (= reservoirs) in Sri Lanka [2] demonstrate how long this strategy has been used in human history.
  2. Diverting water from water-rich areas to water-scarce areas, such as the Roman Empire did it with its aqueducts [3].
  3. Tapping new sources, e.g., by milking clouds [4], desalinating seawater [5] or by using fossil groundwater sources [6].
  4. Efficient use, e.g., through using water-saving shower heads, low-flush toilets, efficient washing machines or drip-irrigation.
  5. Recycling and reusing water, e.g., by reusing treated wastewater for irrigation [7].

Strategies 1-3 completely focus on satisfying a given demand and pay little attention to the ecology of the areas affected by their measures. Due to humanity’s eternal thirst, too many rivers don’t reach the ocean anymore [8][9], and too many mountain areas are running dry. This aggravates the ecological situation there and effects the living quality of people in these areas. You can’t swim or fish in a dry river and hiking in a dry forest without birds is not a funny recreation. Strategies 4 “efficient use” and 5 “recycling/reuse” usually don’t consider ecological issues, but aim for supplying more people with a given amount of water.

In my view, we need a sixth strategy, based on an ecologically engineering way of design. Maybe it’s time to let the old ways (in their pure form) die…

What can ecological engineering contribute to a more sustainable practice regarding water use? It promotes the importance of system’s thinking in the design process. The adoption of a holistic system’s view is crucial in my view, and may lead to painful (but necessary) changes in the way we design our water systems!

For example, the current water-based sanitation- and urban drainage systems require a constant flow of water, lest the sewers start clogging. Water-saving devices are a commonly suggested method to save water. However, less water in the sewers leads to more sediments, which may eventually clog them and need to be removed. Usually this is done by pumping a lot of water from a truck into the sewers by the maintenance crews. Thus, without rethinking the sewer system as a whole, water-saving devices may even turn out to be technically counter-productive.

A holistic system’s planning aims to integrate the whole urban watershed – including water supply and urban drainage – with the needs of surrounding ecosystems into the planning process. It aims to be multi-focused: Hygiene, sanitation, cooling issues, drainage, food production and the recycling of nutrients in urine and fecal matter should all be considered.

An ecologically engineered urban water system should aim to treat (or even better: reuse) any remaining wastewater on-site. Its main feature is the avoidance of wastewater as much as possible. The remaining volume of wastewater should be so small that it can be easily treated on-site, e.g., on a roof, in a facade or in the garden with natural means.

Within the houses, the water system should be inspired by the vision of a closed cycle. This is possible if a) human feces and urine are completely kept out of the water cycle and treated separately, and b) if household chemicals are made “fit for circular systems” (which currently isn’t the case).

In my view this is the necessary next step! But how can it be done? Well, regarding ecological sanitation, a lot of basic work has been done in the past 20-30 years (e.g., [10]). However, there’s still space for a lot of ground-breaking, disruptive innovations here.

If you like to continue to think with me, stay tuned with this blog.



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