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How Water Use Has Declined With Population Growth

Water use has not gone up as population increased in the last few years, contrary to popular opinion and expectations. How does this impact how urban water managers are planning?

Written by Padma Nagappan Published on Read time Approx. 6 minutes
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Rebates for low-flow toilets are on display at Lowes in San Bruno, California. Increases in conservation and efficiency have helped decouple population growth from water consumption.Tara Lohan

Until 1980, water use went up steadily as population increased, necessitating investments in infrastructure and boosts to capacity. But since then, there has been a dramatic decoupling across the United States, with water use declining even as the population and the economy continued to grow.

The U.S. Geological Survey found that water consumption peaked at 440 billion gallons (1,665 billion liters) per day before dropping in 1980 and then remained steady through the 1980s and 1990s. It rose slightly in 2000, but significantly declined between 2005 and 2010, when it fell to 350 billion gallons (1,325 billion liters) per day. The USGS attributes this decline to better cooling methods that cut water use for thermoelectric power, and water use efficiencies in irrigation for farming, improved standards for many appliances and fixtures and laws requiring low-flow fixtures.

“Back in 1980 toilets used 6 gallons [23 liters] per flush, but now it’s 1.2 gallons [4.5 liters] in California. These standards have allowed our economies to grow while our communities grew too,” says Heather Cooley, director of the Water Program at the Pacific Institute. “Another reason is the passage of the Clean Water Act, which tried to reduce impacts of waste discharge, that drove efficiency improvements in industry.”

But despite the public and industry adopting efficiency practices, most of us continue to think water use will keep increasing as population grows, so water agencies have planned for it.

“Emphasis has been on building more supply to meet increasing demand. But if water use remains stagnant, that might mean we invest in facilities we ultimately don’t need, or pay for supplies we don’t need,” Cooley points out.

Improve Demand Forecasting

These developments, and the USGS data that showed declines across the board, prompted Cooley and her colleagues to study these trends and put together a community guide for evaluating future urban water demand.

After examining water use data and water agencies’ urban water plans, Cooley and her colleagues found that while water use stayed stagnant or declined in some areas, many utilities were projecting increased water use in the future, which shows they’re not allowing for efficiency improvements and so they could be overestimating demand, which could increase costs for rate payers for water they may not use.

“So we need to improve demand forecasting approaches,” Cooley says. “None of us has a crystal ball, but we can look at trends for the last 20 to 30 years, and use that to calculate water needs, which will help us to develop a much more sustainable water future for California.”

Part of that forecasting is planning for climate change and its impact on demand, something that she says many water agencies have yet to incorporate successfully.

For each area, water forecasting can look very different depending on local variables.

Water Use Stays Steady in L.A.

A Lowes in San Bruno, California, sells “waterwise” plants to help residents use less water in their gardens. Mandates and incentives to conserve have helped keep water use steady or declining even as population has increased. (Tara Lohan)

A Lowes in San Bruno, California, sells “waterwise” plants to help residents use less water in their gardens. Mandates and incentives to conserve have helped keep water use steady or declining even as population has increased. (Tara Lohan)

The Los Angeles Department of Water and Power (LADWP) has seen the city keep its water demand at about the same level for the last 45 years, despite population going up by 1 million people, thanks to conservation measures, incentives and mandates to cut down on use and rebates to switch to more efficient appliances.

“When actual water demands are lower than our projections, the reasons are not necessarily a reflection of overplanning,” says Martin Adams, interim COO of LADWP. “It has more to do with responses coming from the rapidly changing state and local conservation mandates, constantly evolving state legislation on water-efficiency requirements for indoor appliances and outdoor landscape, and impacts and responses to prolonged drought, which we may not be able to forecast.”

Like most water agencies, LADWP has an urban water management plan that it updates every five years, and adapts as conditions change. Asked if it will change how it plans for the future given the downward trend in water use, Adams said it will take into consideration all factors that affect demand forecasting, including population growth, economy, price of water, climate change impacts and operational flexibility.

“We believe our planning methodology has and will continue to serve the city well, and we will continue to update our plans regularly to adapt to evolving conditions,” Adams says.

Progressive Measures Lead to Big Drop in San Francisco

Up north in San Francisco, the city’s Public Utilities Commission (SFPUC), home to its water, sewer and power departments, has seen water use drop 17 percent for its retail customers between 2005 and 2015, with per capita use falling from 61 gallons per day to 44 gallons per day (230 to 167 liters per day) – at the same time that its population increased by 10 percent.

“These numbers are not an accident,” says Paula Kehoe, director of water resources with SFPUC. “We attribute it to decades of efforts in water conservation and education programs.”

San Francisco also has in place its own ordinances, such as a requirement that if a home is resold, it has to have low-flow fixtures in place before the sale goes through – a rule that ensures older homes (with water guzzling fixtures that might otherwise not get upgraded) also toe the line.

The utility recently completed its 2015 urban water management plan that forecasts for the next 25 years, and it’s projecting a slight increase in water demand as a result of increased jobs and population.

“Part of the reason is that we’ve been doing conservation for over two decades here, so we don’t have as much of an ability to conserve as we look to the future,” Kehoe explains. “What’s important to note is that our per capita will remain the same from now through 2040.”

But does this increased demand call for increasing capacity?

“No, it calls for continuing conservation, converting the remaining older fixtures, recycling water and diversifying supplies,” she says. “We’ve also taken other steps to use water as efficiently as possible. We collect and treat all black water in our SFPUC buildings, and use it for toilets, so we’ve been able to establish a program to get other buildings to do this.”

A 2015 ordinance requires new developments with more than 250,000 square ft (23,000 square meters) to assess gray water that would be produced on site and offset that supply for toilet flushing and irrigation.

Engaging the Public

Kehoe says the agency has had a progressive outlook, and always engages the public in its long-term planning, since part of the plans involve asking the public to take action and reduce water use – outreach that the Pacific Institute’s Cooley says other water agencies need to do.

It has to be a way of life, so public outreach is key to making it happen, says Suzanne Gautier, communications and public outreach manager with SFPUC.

“We have campaigns on newspapers, TV, radio, the Muni and public transit,” Gautier says. “Some of those partnerships have included many of our hotel customers. Water use here is not just a San Francisco conversation, but elsewhere too, so our model can be used by other communities.”

Despite gains made by cities like San Francisco, we still have a long way to go, given the ongoing drought and uncertainties with climate change.

Cooley says that while lower water use shows we’ve made huge strides in efficiencies, there’s always room for improvement and opportunities to look at recycled water, stormwater capture and better management of groundwater, which is severely overdrawn in California.

“If you look at our water use compared to Australia or Israel, we are still using a lot more than what they are. We’ve come a long way, so we should celebrate the success we have had, but we need to keep doing more,” Cooley concludes. “The good news is there is a lot of opportunity to improve.”

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