Climate change is having a real impact, cities can run out of water.
A real shortage of water is now quite common. South Africa is a case in point where the authorities really left it too late to react and almost all traditional sources pretty much dried up, they were just lucky e getting some rains before they ran out water.
South-Western Australian is one of few areas worldwide where all of the global climate models (about a dozen or more) seem to agree that their climate has changed and it is getting driver get drier and drier. Essentially what you see this in the data over the last ~30 years, Perth and South-Western Australian seen the runoff into dams dropping by 30% to 50%.
Perth is probably one the most telling areas that illustrate the impact of climate change. They don't talk anymore about droughts, they're talking about reacting to a drying climate, unambiguous climate model evidence confirms this.
Reacting to a drying climate.
Australian cities have reacted to the challenge by building desalination plants, Perth has two, this works for most of the Australian population because they predominantly live-in coastal cities.
The next step has been to build large water recycling plants that treat wastewater and can return treated water back into the system. Water does not have to be treated to human consumption (Potable) levels, it can be treated to a level suitable either for use in agriculture or reinjection back into aquifer depending upon circumstances.
Treating wastewater to achieve a Potable standard may not be the most sustainable solution. If circumstances allow, water can be treated in a manner to recycle and reuse some of the nutrients, you might as well leave the nutrients in because agriculture needs the (phosphorous and nitrogen) neutrons anyway. Essentially this recycling approach requires big schemes, and we see them being built “everywhere”. They require a centralized approach because of the economies of scale.
There is also a place for decentralized/hybrid solutions, these hybrid solutions can sit in a network. One concept is sewer mining, if you have a big demand somewhere or maybe a sporting field or golf course and don’t need necessarily drinking water treatment for lawns tapping into a sewer feed system to recover water to the standard required by this application is a way of recycling