Designing cities and buildings for drought resilience

An engineered wetland water treatment system at the San Francisco Public Utilities Commission headquarters.

Drought is challenging communities in California and much of the West to rethink how they use water. This time, communities are not looking to large, distant reservoirs but to micro-solutions distributed throughout urban landscapes.

California has mandated a 25% reduction in water use in urban areas. Four straight years of drought mean that the public has been asked to change how they think about and use water. The statewide response to Governor Brown’s mandate has been dramatic, with California reducing potable water use by over 27% in the five months since the emergency declaration. Most communities were able to rise to this challenge, and some were able to even save much more as shown in this New York Times interactive graphic. This response was achieved by raising drought awareness and by local communities crafting a response to best meet their unique needs.

San Francisco recently passed an ordinance mandating on-site treatment and water recycling in large new buildings – the first city in the country to take such a step. Now developments more than 250,000 square feet are required to treat water sources such as graywater, rainwater and foundation drainage on-site and reuse it in the building for toilet flushing and irrigation. These on-site water systems reduce potable water use and stretch the city’s drinking water supplies. These small and distributed systems allow buildings to safely reuse water on site, reducing potable water use in residential buildings by up to 25% and in commercial buildings by up to 75%, and increasing the community’s water supply resiliency.

This realization means that new buildings are looked at as a source for water. Water types that can be generated or harvested from a building include graywater, blackwater, rainwater, stormwater and foundation drainage. Water from our showers, washing machines, and bathroom sinks, collectively known as graywater, is the cleanest and most abundant on-site water source. When treated, it provides a consistent non-potable water supply. While non-potable water is not safe for consumption, it can be used for other purposes such as toilet flushing, irrigation, and laundry. Capturing and treating non-potable water more efficiently matches supply and demand and reduces potable water use. San Francisco is mandating this, and it is likely that other communities will evaluate similar solutions to reduce future water use.

The drought and new conservation requirements like this San Francisco ordinance mean that I’m discussing the future of development and water a lot these days. In many circles, people believe that the era of inexpensive and seemingly limitless water is a thing of the past.

Developers across California are looking to future approvals. The big water question is will a business-as-usual approach work? Many developers are finding that the public’s primary opposition is related to water supply. In response, AECOM is working to develop low-water-footprint communities by using a water balance approach that looks at a site’s water supply and demand (both potable and non-potable) to recommend the most efficient method to manage water on site. This allows developers to best match supply and demand to reduce water use and ensure public support.

Building drought-resilient communities will be a great challenge in coming years. And the one thing that I know for sure is that the conversation is just beginning.

Kerry Rubin is an ecological engineer with AECOM.