Around half of the clean water that our cities consume goes down the drain and into our sewage treatment plants. Here the wastewater from domestic use, agricultural and industrial processes is treated and cleaned, removing solids and impurities. This treated sewage water is called Reclaimed Water or Recycled Water.
The conventional sewage treatment plants are designed to clean wastewater so that it doesn’t represent a threat to the environment or the public health. Ones cleaned, the water is reused in sustainable landscaping irrigation, to recharge groundwater aquifers and to meet commercial and industrial water needs. Many conventional sewage treatment plants process the sewage effluents to a very high degree with advanced water treatment technologies, purifying the water before it is released in to a river, lake or groundwater system used as drinking water supply. The purified water loses its potable properties once it is mixed with nature and in order to be used as drinking water it needs to go through another re-cleaning process.
Reusing highly treated municipal sewage effluents is not a new idea. This process is called Indirect Potable Reuse (IPR). Planned IPR systems have been an important water supply strategy for a number of decades. A more energy efficient alternative exists and is known as Direct Potable Reuse (DPR), this approach is growing rapidly in countries such as the US, South Africa, Australia and Singapore.
DPR uses treated municipal wastewater from a sewage treatment plant and continue to process it to a quality suitable for human consumption, re-depositing it directly back into a drinking water distribution system. It differs from IPR by not discharging the water back to an environmental system, such as a river, lake or aquifer, prior to re-extracting and reusing it for drinking water supply.
From 1968 the only DPR in the world operated in Namibia, but recently new initiatives in different parts of the world are starting to appear, one of the most famous one is NEWater in Singapore.
One of the many advantages of the DPR approach is that it is far more energy efficient than other water sources, not only because it eliminates the re-cleaning process that IPR requires but it also makes water available much closer to the location of the end consumer. When using other sources, water needs to be transferred over long distances, usually up-hill to a suitable lake storage or aquifer recharge site. Pumping water is a highly energy intensive process. Depending on the mix of energy used, the pumping of water generates significant amount of greenhouse gases directly associated with climate change.
Even though Direct Potable Reuse has been considered one of the cleanest most energy efficient and sustainable water sources, it has met a lot of resistance from the general public. The biggest challenge for “Toilet to tap water”, as the critics call it, is not technological or legislative, but psychological. Studies have repeatedly shown that people have a strong dislike to consuming potentially contaminated water. The “yuck factor” applies even when we know the water is clean.
To learn more about the recycled wastewater process and take part of the results of a study to understand and overcome the “yuck factor”, read and listen to these interviews:
Buzz Feed made a funny and revealing video showing the immediate reactions people have when drinking recycled sewage water for the first time.
The overall projection is that recycle sewage will be a normalized source of drinking water in cities around the world. Much of the infrastructure and technology is already in place and now it’s up to us to get used to it.
In our next blog we are going to take a closer look at NEWater in Singapore, as a positive example where the government is working together with scientists to introduce and gain acceptance for the use of recycled sewage water.