Lately, I’ve been thinking out the relationship between urban form and drinking water. Many regions around the world are wrestling with limited supplies of potable fresh water for human consumption. The pressure on drinking water as a resource is immense – we rely on abundant clean water to grow crops, prepare food, bathe, assist in industrial processes, and keep ourselves hydrates. It is an understatement to say that we rely on clean water for our daily existence; it is something we take for granted routinely.
On the surface, this may appear to be a classic environmental resource problem: if we can reduce water consumption to come inline with the recharge rates of water supply systems, then perhaps the problem can be solved. Indeed, water conservation plays an important role as there are tens of thousands of old water fixtures such as washing machines, toilets, shower heads, and faucets that discharge wasteful amounts of water. However, this framework cannot address the constant growth of urban populations.
There are two ways to think about this problem through the lens of urban form:
At the regional scale
If we need to carefully manage our supply of potable water, then we need to think critically about the areas where people can tap into the water system. Water, like other forms of infrastructure (roads, electricity, &c.) can induce development at the periphery of the urban area. When developers know they can tap into large municipal systems, it simplifies their pro-forma.
If regional leaders want to manage the water supply to ensure that future generations enjoy the same resource, then it may not be in the public interest to encourage continuous expansion of municipal water utilities into the hinterlands. While water is generally managed as a public utility, existing users typically bear the burden of costs while new users are subsidized.
One way to re-align costs with users is to institute development impact fees. In many states these fees can be calculated so that new users help cover the cost of new infrastructure required for the operation of the water utility. Another way is to establish a boundary for urban growth as many cities in Oregon have established.
At the neighborhood scale
Conventional suburban neighborhoods built during the second half of the twentieth century often had expansive lawns, two-car garages, and the occasional swimming pool. Each of these features leads to high levels of household water consumption. In most climates, lawns require regular watering to stay green; cars accumulate dust and require washing; and swimming pools demand thousands of gallons of water each.
If new neighborhoods were designed differently, it is possible that we could dramatically reduce household water demand. Urban neighborhoods often exchange private lawn space for public parks; redundant cars for bicycles; and backyard pools for community aquatic centers.
From a natural resource perspective, I am attracted to neighborhood scale solutions for our regional water shortages. This solution becomes hard-wired into the urban fabric and very difficult to reverse. Once a neighborhood is built, it should last for generations. This will reduce demand per household for water over a very long time horizon.
A Design Experiment
I am curious about how much household water demand is affected by neighborhood design. In order to understand it better I propose form of inquiry by design. What if we designed two neighborhoods for approximately 500 homes each. Using the following parameters:
Conventional Subdivision Design
- each house has a private lawn with 6,100 s.f. of grass (there are no public parks) [source]
- one seventh of the homes (71) have a swimming pool (there is no community swimming pool) [source]
- each house has a two-car garage (road infrastructure makes biking and walking nigh-impossible)
Water-Conscious Neighborhood Design
- the neighborhood has 14 acres of well-maintained public park land [source]
- half of the homes (250) have private lawns with 800 s.f. of grass
- one large, indoor community pool is available to everybody in the neighborhood
- one percent (5) of the homes have private swimming pools
- the neighborhood’s transportation infrastructure supports biking, walking, and public transit, thus:
- twenty percent of the homes (100) have two-car garages
- sixty percent of the homes (300) have parking for a single car
- twenty percent of the homes (100) do not have a car
Under this thought experiment, households in the water-conscious neighborhood would use approximately 76,000 less gallons of water than the conventional subdivision. The annual water savings break down as follows:
- 36.2 million fewer gallons of water needed for watering grass (the savings from the neighborhood having 73.2 fewer acres of lawn to water, assuming watering 1″ depth 26 weeks per year [source])
- 1.0 million fewer gallons of water needed for pools (the savings from 66 fewer private pools to fill 18,000 gallons each [source] after subtracting the additional 188,000 gallons needed for the community pool [source], not counting evaporation losses from outdoor pools)
- 0.96 million fewer gallons of water needed for washing cars (the savings from 500 fewer cars to wash assuming 160 gallons used once per month to wash a car in a driveway [source])
It seems clear to me that neighborhood design plays a significant role in this natural resource question. Indeed, researchers have looked at this question using scientific analysis and found similar results. It appears that community design plays a substantial role in our demand for water.