But now, Wibulpolprasert knows more than most people about Durham’s water use: Because of a research project she undertook, she can tell you what kinds of households in Durham use the most water.

“This is the first time I applied theory to the real world,” she said.

One of Wibulpolprasert’s conclusions was that people in new homes use considerably more water on average than people in older homes, even when she took into account other factors such as lot size, family size and ownership status. Another finding: People with higher incomes use more water on average, again controlling for other factors.

But the connection between water use and income reinforced an assumption she had going into the project she said: “The richer would use more water.”

Becker, who taught the Urban Economics course and advised Wibulpolprasert on the project, said her research looks at some key issues.

“What is a realistic target for water reduction? That is the real question,” Becker said about the topic. “There’s virtually no analysis of individual water use, not just in Durham, but across the country.”

Wibulpolprasert’s report has policy implications, he said.
“Her work reinforces the argument for a rational conservation plan with little or limited impact on the poor that involves rising [graduated] price rates,” he said.

Analyzing the data was only one part of Wibulpolprasert’s project. She first had to get them. That meant making repeated visits and phone calls to the City of Durham’s customer billing department to request residential water use data in an electronic format she could manipulate. Her persistence paid off, and she obtained water department billing records for 5,000 households for July 2007.

She then downloaded block-by-block demographic information about Durham households from the Census Bureau’s American FactFinder website. She got statistics on factors she thought might be affect water use: family size, lot size, income, race, age of householder, age of house, ownership status, house value and rooms per house. She then used statistical software to perform a mathematical analysis called regression that isolates the influence of each factor while controlling for all the others.

“Very few people -- even graduate students -- will be involved in getting data from a [primary] source,” Becker said. “For Wichsinee to have done that is a major task.”

Both Becker and Wibulpolprasert acknowledge limits to the study. The major one involves a statistical feature called variance. The two found that water use fluctuates greatly even among households with similar demographic profiles. The factors they could identify as having an effect -- family size, income, lot size, value of house and age of house -- explain only a very small proportion of an individual resident’s water consumption. The rest appears to result from variables they were unable to measure, or from idiosyncratic personal preferences.

“We’d never figure out exactly who are the people obsessed with keeping their lawns green,” Becker explained.

One resident has certainly been persuaded by the study -- Wibulpolprasert, who lives an apartment on Central Campus. She said she has begun adopting water-saving measures such as using hand sanitizer without water to wash her hands, not running the water while washing dishes and even cutting off the shower when soaping up. 

“I keep telling people to conserve water,” she said.