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.



Sustain ability!!!

We should look with awe at the immense ability of Earth’s biosphere to sustain itself. In the millions of years of life on Earth, this ability always persisted. This is why life (and therefore humanity) is still around today. The biosphere has been resilient enough to weather several mass extinctions of global scale in its geological past, e.g., caused by asteroid impacts [1].

Can humans have an impact on Earth’s biosphere to the extent of an asteroid? I think so. If we’d really wage a war with nuclear weapons, the effect might be comparable. But even without such a disaster, we are now testing the limits of the current state of the biosphere.

Ecological science has documented numerous cases, where ecosystems irreversibly passed tipping points due to human activities [2]. A small example is Lake Sempach in Switzerland, which happens to be in my neighbourhood. Ever since a massive fish kill in 1984, caused by eutrophication, is has been artificially aerated. Even today (2018) there are still no prospects for completely switching off aeration.

When a certain threshold is passed, it is difficult or even impossible to revert an ecosystem to its previous state. Does the biosphere as a whole also have such tipping points? Ecology suggests that it does.

Sustainable development is an expression whose meaning is somewhat difficult to grasp. It is often defined as development that “meets the needs of the present without compromising the ability of future generations to meet their own needs” [3]. But what does “ability of future generations” mean? Let’s illustrate this with an image.

If humanity were a weightlifter, sustainable weightlifting would mean that we’d not ever be allowed to put down the dumbbells*. A threshold effect, such as a climate tipping point, would continuously put more weight on the dumbbells. Unexpected disturbances would weaken the weightlifter. Even a trained weightlifter would eventually break down.

Ability of future generations implies the “capacity, fitness, or tendency to act in a (specified) way” ([4]) to meet their needs. We should lighten the burden of our kids and our grandchildren instead of adding the weight of an irreversible ecological change to it. I also think we need to teach and train them how to engineer their direct environment holistically and based on findings from ecology. Sustain ability with Ecological Engineering!


* this type of weightlifting is fortunately not an olympic discipline…


[2] Resilience Alliance and Santa Fe Institute. 2004. Thresholds and alternate states in ecological and social-ecological systems. Resilience Alliance. (Online.) URL: