What is the Water Table?

Water doesn’t only exist in lakes, rivers, and oceans.

A vast amount of water is also hidden beneath our feet.

The term water table refers to the level underground where the soil and rock become completely saturated with water.

This invisible boundary is important for many reasons.

By understanding what the water table is and what influences it, homeowners can better manage groundwater issues and protect their properties.

What is the Water Table?

The water table is essentially the depth in the ground at which groundwater begins.

Formally, it’s the boundary between two zones: the unsaturated zone (above) and the saturated zone (below).

In the unsaturated zone, soil and rock contain air pockets along with some moisture.

In the saturated zone beneath, all the gaps and pores in the soil or rock are filled with water.

If you dig into the earth, the water table is the point at which the hole you’re digging starts to collect water at the bottom.

A simple example is digging in sand near a beach: as you dig down, you’ll eventually see water seeping into the hole, marking where the ground is saturated.

Above the water table, the soil might feel dry or just damp; below the water table, the ground is completely soaked.

The depth of the water table varies widely from place to place and can change over time.

In a low-lying marsh or after weeks of heavy rain, the water table might be just below the surface, this can lead to things such as waterlogged lawns.

In contrast, in an arid area or on a hill, the water table could lie many metres deep.

In fact, even within a single property the water table can fluctuate with weather and seasons, sometimes rising or falling significantly throughout the year.

The Science Behind the Water Table

Beneath the ground, water from precipitation (rain or melting snow) slowly soaks downward through soil and rock.

Gravity pulls this water deeper until it reaches a level where the ground can hold no more water.

This is where the saturated zone begins, and that upper surface is the water table.

Everything below that level is effectively underwater, filling the pores and cracks in soil or bedrock.

The geology of the area plays a role in how this happens.

For instance, sandy or gravelly ground, which has large connected pores, lets water through quickly, whereas clay or solid rock layers may block water flow.

In many places, an impermeable layer of rock or clay lies beneath the groundwater, so the water accumulates above this layer, saturating the materials above it.

The saturated zone where water collects and moves is what hydrologists call an aquifer, which is essentially an underground reservoir.

Water Table Shape

The shape of the water table isn’t usually flat like a tabletop; instead, it tends to rise and fall following the contours of the land above.

Under a hill, groundwater may be at a higher elevation (because water infiltrated at the top of the hill adds to the groundwater there).

Whereas under a valley the water table often dips lower.

Groundwater slowly flows from these higher recharge areas to lower areas, much like how surface water flows downhill.

However, groundwater moves very slowly compared to a surface stream.

How fast it travels depends on the type of rock or soil.

It might move several metres per day through coarse gravel, or only a few centimetres per year through dense clay.

Eventually, this underground water finds its way out.

If the water table intersects the ground surface, the groundwater emerges as a spring, seep, or marshy area.

Such outflows often feed streams, ponds, or wetlands.

This is why even in a dry spell you might find some water flowing in a creek.

The Water Cycle

It’s also important to note that the water table is part of a larger system – the water cycle.

Water that soaks in from rain and snow is what replenishes the groundwater over time.

Plants and evaporation can draw water out of the soil above the water table.

This can influence how much water percolates down to the water table.

What Affects the Water Table?

There are many factors that can affect the water table, and they can be broken down into natural and human factors.

Some of the main ones are:

Natural Factors

Several natural factors influence the level of the water table.

Rain

Rain is one of the biggest drivers.

After a period of heavy rain, the water table will typically rise as more water seeps down into the ground than usual.

Conversely, during a drought or extended dry spell, the water table can drop because groundwater isn’t being replenished as fast as it’s being used or drained away.

Seasons

Seasonal changes have a noticeable effect.

In late winter and spring, melting snow and rainfall add a lot of water to the ground, often causing a rise in the water table.

In the summer, especially in vegetated areas, growing plants draw significant moisture out of the soil.

This process (through plant roots and evaporation from soil) can lower the water table during hot, dry months.

Temperature

Temperature also plays a role; warm weather increases evaporation from the land surface.

This potentially reduces how much water percolates down.

Soil Type

Soil and rock characteristics are another key factor.

Different soils have different abilities to absorb and transmit water.

For example, sandy or loamy soils allow water to infiltrate easily, which can recharge the groundwater quickly.

Clay-heavy or dense soils, on the other hand, might prevent water from moving down, causing it to puddle at the surface or create perched water pockets.

In areas with very dense, absorbent soil, water tends to linger near the surface, whereas in areas with fast-draining soil, the water can sink deeper before fully saturating the ground.

Topography

Topography will influence groundwater flow as mentioned.

Water tables often mimic the rises and dips of the landscape.

So low-lying areas like valleys or flat plains might naturally have a shallower water table (closer to the surface) than steep, elevated areas.

Lakes and Rivers

Nearby bodies of water also affect the water table.

If your property is near a lake, river, or marsh, the water table in the ground will often align somewhat with the surface water level.

In fact, the lake or river can be thought of as an exposed part of the water table.

During periods when rivers run high, the adjoining groundwater can also rise, and if the river level drops, it can draw down the adjacent water table with it.

Human Factors

Human activities can significantly impact the water table as well.

Groundwater Extraction

One major factor is groundwater extraction.

When people drill wells and pump out groundwater for drinking, irrigation, or industrial use, they are pulling water from the saturated zone.

If water is pumped out faster than it is naturally replenished, the local water table will fall.

In the immediate vicinity of a heavily pumped well, the water table can even form a downward dip (often called a ‘cone of depression’) as water levels drop around the well.

If multiple wells in an area withdraw large amounts of water, the overall regional water table can be lowered over time.

In extreme cases, excessive pumping has caused long-term declines in groundwater levels, as seen in parts of the world where aquifers are being depleted faster than they recharge.

Development

Changes to the land’s surface can also affect how water enters the ground.

Urban development often creates vast areas of hard, impermeable surfaces like roads, pavements, and rooftops.

These impervious surfaces prevent rainwater from soaking into the soil.

Instead, the water runs off into drains or rivers, meaning much less reaches the groundwater.

This can lead to a lowering of the water table under cities or developed areas because the natural recharge from rainfall is reduced.

Agriculture

Conversely, certain human practices can raise the water table.

For instance, agricultural irrigation adds a lot of water to the land.

If crops or soil don’t use all that water, the excess can seep down and raise the water table over time.

How Can the Water Table be Controlled?

While we cannot control large-scale groundwater levels, there are steps homeowners can take to manage a high water table and mitigate its effects.

The goal is usually to keep water away from vulnerable areas (like your home’s foundation) and encourage groundwater to stay at a safe level below your structures.

Here are some common measures:

Improve Drainage Around the Property

Good drainage helps prevent water from pooling and seeping straight down near your house.

This can involve landscaping adjustments such as sloping the ground (grading) so that surface water flows away from the foundation.

Additionally, installing swales or shallow ditches can channel excess rainwater to a safe outlet.

In many cases, homeowners install French drains, perimeter drains or even sustainable drainage systems.

These are essentially perforated pipes buried in gravel trenches that collect and redirect groundwater away from the house.

These drains, sometimes called ‘weeping tiles’, intercept water in the soil and carry it off before it can rise to floor level.

Keeping your gutters and downspouts in good condition is also important.

Ensure that rainwater from the roof is directed well away from the foundation (through downspout extensions or drainage pipes) so that it doesn’t contribute to raising the water table right next to your basement walls.

Use Sump Pumps and Internal Waterproofing

In areas prone to a high water table, many homes have a sump pump system.

A sump pump sits in a pit (sump basin) usually in the basement or crawl space.

As water from the ground collects in this low spot, the pump automatically kicks on and pumps the water out and away from the building.

This actively lowers the water level immediately around the house.

Along with a sump pump, an interior drainage system might be installed.

For example, a drain tile or channel along the inside perimeter of the basement footing that directs incoming water into the sump pit.

By constantly capturing and pumping out groundwater, these systems can effectively keep the water table below the basement floor.

It’s also wise to waterproof basement walls (using sealants or membranes) as an extra line of defense.

While such waterproofing doesn’t actually lower the water table, it helps keep any near-surface groundwater from penetrating into the basement.

Subsurface Drainage and Dewatering Systems

For properties like large yards or agricultural land where a high water table is a broader issue, owners sometimes resort to subsurface drainage networks.

This is similar in concept to the French drain, but on a wider scale.

It is a series of perforated pipes buried throughout the area to actively lower the groundwater level.

In farming regions with waterlogged soils, tile drainage systems have been used for decades to lower the water table and dry out the soil for crops.

In extreme cases (such as during construction projects or in very water-logged terrain), temporary dewatering wells or pumps can be installed to continually draw down the groundwater.

These solutions typically require professional design.

On a smaller residential scale, however, such aggressive measures are rarely needed beyond a good drainage and sump pump setup.

Key Takeaways

You should now have more of an understanding of the Water Table.

The water table is a fundamental concept in understanding groundwater.

It is the depth below ground at which the earth is saturated with water, and it can move up or down depending on weather, seasons, and human activities.

For homeowners, the water table is more than just a theoretical line on a diagram.

It can determine whether you have a dry, sturdy house or a damp, flood-prone basement.

A high water table can create challenges like wet yards, structural pressures on foundations, and unwanted water intrusion into living spaces.

By being aware of the water table in your area, you can make informed decisions, such as how deep to lay your foundations or whether you need additional drainage.

For more information on the water table, or help with any and all of your drainage needs, get in contact with us here at KD Drainage.