In Kenya, water insecurity is a life-threatening reality, and the population is expected to leap from 40 million to 60 million in the next twenty years. Most of the country still depends on wood and charcoal for household energy, and forest cover is dwindling. At the same time, the climate is changing: rainfall is decreasing, river levels are low and water contamination is on the rise. In the fierce competition for shrinking resources, the most vulnerable are women and girls, who are responsible for finding water and fuel for their families. At dawn, nine-year-old Anzelma walks for miles in search of firewood. Many in her village have died from drinking dirty water, and firewood is a valuable commodity, used to boil water to make it safe. Anzelma’s small body bends under the heavy loads of wood balanced on her head, but she knows her long journeys into the forest are crucial for her family’s survival. One company is attempting to change this by providing 900,000 water filters to the people of Kenya’s Western Province, for free. This is the largest household water treatment program in the developing world, and it’s being financed with carbon credits earned through the reduction in use of firewood. If successful, it will cut carbon dioxide emissions by 2 million tons per year for a decade or more. But it requires changing the habits of 4.5 million people first.