Nearly half a million Rohingya people have crossed into Bangladesh in the last four weeks. More than a quarter are pregnant women, new mothers and children under five. Families are crowded together in makeshift camps, without adequate shelter and access safe drinking water. If they are lucky, they may have some plastic sheeting to sleep under, but most of the time they are huddled under sarongs. Having just crossed a torrential river to reach the camps, these families are now confronted by pouring rain and flooding, and the risk of waterborne diseases is alarmingly high. Women and children are particularly vulnerable in the camps, sleeping under open skies, on roadsides and in forest areas with little or no protection. We are on the ground responding to the immediate crisis. Together, we plan to reach more than 200,000 families with clean drinking water, portable toilets, sanitation facilities, tarpaulins and other essential supplies. A humanitarian flight carrying 15 tonnes of supplies left our warehouse in the United Kingdom on Friday, with water pumps, material for construction of emergency toilets and water tanks. Two more humanitarian flights are planned with additional supplies. We can prevent the worst from happening. But we must act now.