Following years of civil war in Liberia, access to safe drinking water and a coordinated health response are at the core of WHO's work in the country.

Carefully, a young man unrolls a long green cord and lets it down a well. Weighted by a stone at one end, the cord has many small knots along its length. The distance between each knot is exactly one foot. "We use this to measure the depth of the well and to calculate the height of the water inside", he explains. To do this, he first counts the number of knots until the stone touches the water. Afterwards he lets the stone down to the bottom of the well and subtracts the difference. "We have to do this in order to determine the amount of chlorine needed to purify the well water", he adds. To clean this particular well, a tablespoon of chlorine is sufficient. His colleague pulls up some water in a bucket, adds the chlorine powder, and throws the water back