Recent disputes over water use in deserts that are well suited for solar thermal power plants have illustrated the need for a holistic approach to urban needs. Solar thermal plants use cheaper technology than photovoltaics (solar panels), but require substantial water because mirrors heat a liquid to create steam that drives an electricity-generating turbine. Similar to a fossil fuel power plant, the steam must be condensed back to water and cooled for reuse. Typically this happens in a cooling tower and requires constant replenishment of water as the excess heat and water evaporates. Alternatively, dry cooling can be used, but requires fans and heat exchangers and is much more expensive.
The American Southwest is currently the site of plans for dozens of multibillion-dollar solar power plants on thousands of acres of desert. In California, solar developers have already been forced to switch to less water-intensive technologies when local officials have refused to give up water. Furthermore, some large solar projects are currently tangled in conflicts with state regulators over water consumption.
Considering the effects of power generation on the ability to provide water for a community will be crucial as water becomes even scarcer and renewable power projects burgeon to replace fossil fuel production.
Using low-carbon technologies that are not water-intensive combined with smart city planning and sound water use policies will help cities to avoid water disputes among stakeholders. Cities around the world have already implemented rainwater harvesting policies to help address water shortages by simply catching and using the rainwater that is currently diverted into storm drains – and ultimately, into the ocean. Moreover, California implemented a new policy at the beginning of 2009 to allow the installation or alteration of a clothes washer greywater system to be exempt from a construction permit that was previously required. Greywater systems allow a household to irrigate a landscape with recycled water.
Employing green rooftops and community gardens in dense cities and maintaining substantial surrounding open space is a strategy for water conservation as well because the less paved or impermeable surfaces exist, the less urban runoff occurs and the more ground water can be recharged. Furthermore, water use intensity is greatly affected by population density. According to the Sierra Club’s Challenge to Sprawl, three households per residential acre (typical suburban sprawl) on average equates to 1,032 gallons of water used per household per day. Conversely, 100 households per residential acre on average equates to 192 gallons of water used per household per day
Such policies will relieve pressure when citizens take advantage of them to conserve and they mean greater efficiency in the use of resources. Policies that force vital human services (such as power production and delivery of water) to compete for the same resources are unlikely to succeed. Moreover, the monetary and environmental cost of water projects like desalinization is substantially higher than simply allowing citizens to catch rainwater or irrigate with recycled water. Thus, tax payer dollars are better spent when policies support sound urban design and resource conservation.
Several city planning and policy experts will be addressing the issue of water use in cities at the upcoming EcoCity World Summit in Istanbul this December. Presenters will include Richard Register of EcoCity Builders, Walter Hood (urbanist, landscape architect), Ken Yeang (bioclimatic design), David Hall (New Vista Ecocity), the World Bank Eco2Cities program, Global Footprint Network, Janet Larsen of Earth Policy Institute (representing Lester Brown’s Plan B), and Brent Toderian, head of City Planning for City of Vancouver, Canada and author of the EcoDensity Initiative.