The 12,000 plus members of Engineers Without Borders have worked on more than 300 projects in over 45 developing countries. Their mission is to "help create a more stable and prosperous world by addressing people's basic human needs by providing necessities such as clean water, power, sanitation and education."
EWB takes on projects that are proposed by a community. It's a grassroots approach that ensures projects are needed by a community and have commitment from community members.
Engineers Bring Better Health to Rural Communities describes a project they took on recently in Honduras to bring clean water to a rural village. Their website describes many more projects.