More than 100 people are dead in El Salvador following days of torrential rain that triggered floods and landslides. Over the weekend, the first emails hit from colleagues. Then wire service stories started showing up in newspapers around the country. This morning, I have spent the past hour emailing with my colleague Tjarda in San Salvador: Thousands of people have flocked to shelters. Some have seen their houses washed away by the raging waters, and many will return home to widespread damage.

It’s hard to fathom the devastation that rain can cause, but in a poor country where many of its seven million citizens live in precarious locations—in low-lying areas prone to flooding, or along steep hillsides whose fronts slip away when water-logged—the destruction can be sweeping.

And one of the worst consequences of flooding is the pollution of drinking water.

We learned how severe a problem that can be earlier this year when we were putting together a video on the effects of climate change and what poor communities are doing to fight back. In some of the rural villages of Zacatecoluca, many families rely on hand-dug wells for their drinking water, hoisting it up in buckets attached to ropes. But when the region floods, as it increasingly does, all kinds of waste sloshes into those wells, contaminating the water and making people sick.

“Healthy wells” are one answer. They’re capped and lined with a filter and the clean water is stored in a big tank from which people can draw. But only a few communities, so far, have these healthy wells. Many more are needed, and the calamity El Salvador is now grappling with reminds us just how critical that need is.

Soon after the disaster struck, Oxfam’s partners in the region began delivering aid to some of the local shelters–from supplies that had been pre-positioned. Check here for updates on Oxfam’s ongoing response.