Beneath our feet there is an invisible ocean. Within the cracks of rock slabs, sand, and soil, this water sinks, swells, and flows — sometimes just a few feet under the surface, sometimes 30,000 feet below. This system of groundwater provides a vital supply for drinking water and irrigation, and feeds into rivers, lakes, and wetlands. Across the globe, it contains 100 times as much fresh water than all of the world’s rivers and lakes combined.

As Earth warms, groundwater — long seen as an immutable resource — is in flux. Most often, climate change is associated with a decrease in groundwater, fueled by worsening drought and evaporative demand. But in some areas, this water is actually creeping higher, thanks to rising sea levels and more intense rainfall, bringing a surge of problems for which few communities are prepared.

Places in the United States where the water table is inching higher — along the coasts, yes, but also inland, in parts of the Midwest — are already beginning to experience problems with infrastructure. Cracks in aging and poorly maintained pipes are being inundated, leaving plumbing unable to carry away stormwater and waste. Pavement is degrading faster. Trees are drowning as the soil becomes soupier, starving their roots of oxygen. During high tides and when it rains, groundwater is even reaching the surface and forming temporary ponds where there never used to be flooding.

This phenomenon — groundwater rise — could also have dire effects on people’s health, exposing them to new or unearthed pollutants. In the San Francisco Bay Area, rising groundwater threatens to spread contamination that can evaporate and rise into the air inside homes, schools, and workplaces. In Beaufort County, South Carolina, it is flooding septic systems, leaching raw sewage into nearby waterways. Along the Vermilion River in Illinois, it is seeping into unlined pits containing coal ash — a hazardous waste — and carrying heavy metals into drinking-water aquifers.

These three communities, profiled below, demonstrate the risks that other parts of the country may soon face as climate change alters a system long taken for granted.

Read the full article about rising groundwater by Julia Kane, Lina Tran, and Diana Kruzman at Grist.