“You need to safely contain the human excreta and keep it free from flies,” says Kamal Kar, a development specialist from Kolkata, India, who devised an approach for encouraging people to build and use toilets that is now deployed in 70 countries. To construct a basic pit latrine, you don’t need engineers, special equipment or much money. Dig a deep hole set back at least 50 feet from drinking water (in some villages a simple six-foot hole was sufficient for a family of six for up to three years). To keep from falling into the pit, install a cover, or “squatting plate,” of wood or reinforced concrete with a hole cut in the middle. A tightly fitting lid keeps insects out. A simple superstructure of wood, cloth or even palm fronds provides basic privacy and shelter.

Two billion people worldwide don’t have access to basic sanitation facilities. Of these, 673 million defecate in fields, rivers or gutters, which makes them and their communities more vulnerable to diseases and conditions like cholera, diarrhea, typhoid, dysentery, polio, hepatitis A and childhood stunting. Two decades ago, in rural Bangladesh, Kar kept seeing unused latrine equipment donated by governments or aid organizations. Realizing that this top-down effort wasn’t working, he devised an alternative known as community-led total sanitation. As part of the process, a facilitator gathers people and asks them to do the following things: calculate how much fecal material they collectively produce in a day; draw a big village map on the ground and mark where they defecate with colored chalk powder or bits of paper; walk together through the outdoor defecation zones. Facilitators also put human feces next to a plate of food in front of the gathered crowd. “You can watch the plate become black with flies,” Kar says.

After this “triggering” exercise, the group designs and implements pit latrines in a way that incorporates their skills and knowledge and uses local materials. Facilitators will offer advice when asked. They might suggest digging a pit with slanted, funnel-like walls to avoid collapse; or lining pits with concrete, bricks or even bamboo slats; or installing a ventilation pipe. “I’ve seen hundreds of models of low-cost, appropriate toilets,” Kar says. “How you build it matters less than whether you use it.”