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How Rising Groundwater Can Affect a Basement

Rising groundwater basement problems begin underground, where the water table is the level below which the soil is saturated with water. After a long wet spell, the water table can rise until it reaches the floor of a basement, and then water can push up through the floor itself, through the joint where the floor meets the walls, or through cracks that stayed dry all summer. The water appears from below rather than from the side, which is what makes groundwater flooding different from rainwater running against a wall.

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Basements are uncommon across most of California, and they exist mainly in older homes and some hillside areas, so groundwater basement problems affect a smaller group of homes. For those homes, though, a rising water table is one of the hardest causes to deal with, because the water is coming from the ground itself rather than from a single leak. The [basement water damage cleanup](/basement-water-damage-cleanup/) page describes the cleanup service in general terms.

What the water table is in general terms

The water table is the level underground below which the soil and rock are saturated with water, and it rises and falls with the seasons. In a wet winter it rises as rain soaks into the ground, and in a dry summer it falls as the ground dries out. A basement floor sits at a fixed depth, so when the water table rises above that depth, the floor is below the water level and water can press upward against it.

No water-table figure is claimed for any place in this guide, because the water table varies widely across California and from year to year. What holds in general terms is that a wet winter raises the water table, and that basements in low-lying ground are the ones most exposed when it rises.

How groundwater enters a basement

Groundwater enters a basement through the floor and the joints, because the pressure is upward rather than sideways. Water can seep through the concrete floor itself, through the joint where the floor meets the wall, or through cracks in the floor that open under pressure. The water often appears in the middle of the floor or along the floor-wall joint, rather than running down a wall, which is a clue that the source is below rather than beside the room.

The flow can be slow at first, appearing as dampness that grows over days, and it can continue for as long as the water table stays high. Unlike rainwater that stops when the storm ends, groundwater can keep coming until the ground dries out, which is why a groundwater flood can last longer than a rain flood.

How Rising Groundwater Can Affect a Basement — California basement water damage guide

Signs of groundwater in general terms

The signs of groundwater in general terms are water that appears from the floor rather than a wall, dampness along the joint where the floor meets the walls, and water that rises after a long wet spell rather than during a single storm. The water is often clear and free of soil, because it has come up through the ground rather than running across the surface, though it can carry silt where it has passed through a crack.

A sump pit that fills even when it is not raining is another general sign, because the pit collects groundwater from below the floor. These are clues in general terms, not a diagnosis, and a professional looking at the home in person can say more about whether groundwater is the source.

Why groundwater flooding lasts longer

Groundwater flooding can last longer than rain flooding because the water table falls slowly, over days or weeks, while rain stops in hours. A basement that takes groundwater may hold water long after the sky has cleared, and the water may keep returning until the ground has dried out. That persistence is frustrating, but it is also a clue: water that stays for days after the rain points toward the ground rather than the sky.

Homeowners should not try to pump groundwater away themselves while standing in it, and should not enter a flooded basement for any reason. The water is not safe water, and submerged outlets and panels make it dangerous. Stay on dry ground and call a professional to arrange a visit.

Groundwater and sump pumps in general terms

A sump pump is the device that handles groundwater in the homes that have one, because it collects water from below the floor and pumps it away. When the water table is high, a pump may run often and for long periods, and a pump that stops during a high-water period can let the basement flood quickly. The pump does not lower the water table; it removes the water that reaches the pit.

For homes with a pump, a high-water period is the hardest test of the year, and a pump that has not been checked before the rainy season is a risk. The [basement sump pump failure cleanup](/basement-sump-pump-failure-cleanup/) page describes the cleanup service in general terms.

What to do about groundwater

When groundwater is the likely source, the practical steps are the same safety steps as any other basement flood: never enter a flooded basement, keep children and pets away, and call a professional to arrange a visit. Do not try to seal a floor from inside a flooded room, and do not handle electrics in standing water. A professional looking at the home in person can say more about what fits that property than any general guide can.

The [basement water damage cleanup](/basement-water-damage-cleanup/) page sets out the service in general terms for California homeowners, and the waterproofing page describes prevention services in general terms.

Key Takeaways

The water table is the level underground below which the soil and rock are saturated with water, and it rises and falls with the seasons.
Groundwater enters a basement through the floor and the joints, because the pressure is upward rather than sideways.
The signs of groundwater in general terms are water that appears from the floor rather than a wall, dampness along the joint where the floor meets the walls, and water that rises after a long wet spell rather than during a single storm.
Groundwater flooding can last longer than rain flooding because the water table falls slowly, over days or weeks, while rain stops in hours.
A sump pump is the device that handles groundwater in the homes that have one, because it collects water from below the floor and pumps it away.
When groundwater is the likely source, the practical steps are the same safety steps as any other basement flood: never enter a flooded basement, keep children and pets away, and call a professional to arrange a visit.

Your Next Step

If this guide matches what you found at home, the next step is a visit — not a guess. Call and describe what you found, and the visit is arranged from what you describe. The Basement Water Damage Cleanup page explains what that service covers, the Basement Flooding Cleanup page covers a related part of the job, and the services hub lists every service in one place.

While you wait, do not enter a flooded basement and do not touch switches, plugs or appliances in standing water. Floodwater is not safe water — keep pets and children clear of it.

Keep the guides on this site bookmarked: the first guide, the signs guide, and the preparation guide cover the checks worth repeating — after moving in, and after heavy rain.

Basement water damage help is available across California. See basement water damage cleanup in Inverness, CA for one local example, or find your town on the service areas page.