"Water Without Borders", Input/Output, ME Departments, February 2007

input/output

by Harry Hutchinson, Executive Editor

Water Without Borders

This is about a connection from one mountain town to another, 10 time zones apart.

In the highlands of Rwanda, the terrain and the economy rule out access to well water. If communities could afford to tap an aquifer, they'd be unlikely to have the money to maintain the infrastructure that would deliver the water. Technology to purify water has to be more efficient than boiling over a wood fire, and at the same time must be sustainable in a remote area of a country where the gross national income per capita is about $1,300.

So residents in the town of Muramba, as so many people do in the developing world, rely on ground water, with all the risks attendant to a water supply open to contamination.

A team of students from the University of Colorado, representing the school's chapter of Engineers Without Borders-USA, pitched in with residents of the town and with students from a nearby vocational school. They came up with a water-purification system that makes efficient use of the landscape to work.

Town water department: Students from the University of Colorado, representing Engineers Without Borders-USA, worked with residents of Muramba, Rwanda, and with students from a nearby vocational school to build a water-purification system that makes efficient use of the hills.

They call it the "Bring Your Own Water" system, and it can provide as many as 7,000 liters a day of potable water. The system consists of a gravity-fed settling tank, rapid sand filter, and a solar-powered ultraviolet sanitation light.

The system is built against a retaining wall. At the top of the wall, a user pours water into a 55-gallon drum containing PVC tube settlers. The water drains into a pipe that feeds into another drum about 12 feet below. The lower drum has layers of filter material—6 inches of gravel, 12 of sand, and another 6 of volcanic stone. Gravity acting on the water in the 12-foot descent forces the water through the filters, which remove most of the particulate matter that carries bacteria. The water gets a second cleansing by passing through an enclosed box where it is exposed to UV light.

One of the engineers on the project was Evan Thomas. A doctoral student in aerospace engineering at the university in Boulder, he works at NASA's Johnson Space Center on water recovery systems. He said it will cost about one-fifth of a cent per liter of water to maintain the system, a cost that the Muramba health clinic will cover because operating the water purification system will deliver health benefits to the community. The main cost will be replacing the UV lamps, which are available through a supplier in Kigali, Rwanda's capital.

According to Thomas, the team has budgeted a replacement of the lamp every six months, although based on expected usage of seven to eight hours day, he expects a lamp to last as long as two years. The power is provided by a 102-watt solar panel.

Using the system is about 20,000 times more energy efficient than burning firewood to boil water, Thomas said.

Max Gold, a grad student in civil engineering, was the lead engineer on the Bring Your Own Water project. He said that to maintain the system, there is a provision for periodic backwash. Next to the intake drum at the top of the wall, there is a second drum. A small amount of the water entering the purification system—between 1 and 2 percent—is diverted to the second drum, where it is stored until needed. A separate pipe can carry this water to the bottom of the filter tank. Gold pointed out that this stream has about 5 meters of head, sufficient to force it back up through the filter media.

The cost of the system, including shipping it to Rwanda, was about $3,000. Trials conducted in Boulder showed that the system can eliminate all the bacteria in a highly contaminated test sample. Gold estimates that an optimized production model of the system, built with local materials, could be constructed for less than $1,000.

According to the University of Colorado, the Engineers Without Borders chapter has participated in a number of improvement projects in Rwanda over the past two and a half years, including the demonstration of a biogas reactor, which can capture methane from animal waste to burn as cooking fuel.

The university said that funding for various projects has come from its own internal sources and from Unesco, the U.S. Environmental Protection Agency, AmCom Insurance, Rotary Clubs, Engineers Without Borders, and other private and grant donations.