Groundwater levels

What is groundwater?

Simply put, groundwater is water that is stored beneath the ground. When it rains, water runs into our streams and rivers and soaks into the soil, which acts like a big sponge. Some of this water is used up by plants and some is returned into the atmosphere through transpiration. Some also makes its way further into the ground permeating through soil and rock and becomes groundwater and part of the water table. There it is stored underground in a layer of porous rock or sediment - known as an aquifer.

Many of the iconic chalk streams in our region, like the Test and Itchen, are fed by groundwater springs, and where these springs form, is often where we see much higher levels of groundwater.

How do we measure groundwater?

We receive updates from the Environment Agency and compile the data from readings taken at our indicator boreholes.

Groundwater is measured in Metres Above Ordnance Datum (mAOD). mAOD is based on the mean sea level at Newlyn in Cornwall and is used as the reference point to calculate height above sea level in the UK.

The graphs below show the latest groundwater levels compared to previous years. The red, orange and yellow lines show how the actual levels compare to what's considered as exceptionally or notably low.

Groundwater flooding

With increasing rainfall averages across our region, it’s easy to see why the water table has risen. So much so, that in some areas, it’s pushed its way up through cracks in the ground, making its way above the surface causing groundwater flooding.

How does it affect our customers?

We live in a very chalky area, therefore we are particularly susceptible to higher levels of groundwater, not to mention we also have our fair share of hilly landscapes. Villages found in valleys are much closer to the water table, making groundwater problems a more frequent occurrence. Because the chalk acts as a sponge, there is often a lag period between rainfall and river flows increasing, this can mean we continue to feel the impact of excess groundwater even when it hasn’t rained for weeks!

But flooding is just one of the issues we're presented with. When groundwater makes its way into the sewer network, we’re met with more challenges. Our sewers were only built to cope with wastewater and can quickly become overwhelmed. Excess groundwater can meander into private pipes, meaning less room for wastewater, leaving our network under immense amounts of pressure.

In the worst-case scenario when this happens, we use tankers to take excess water out of the sewers and treat it at our sites. This reduces the pressure on our network and the risk of foul sewer flooding. However, this is only a short-term, emergency solution.

Long term, what we can do is make sure our sewer network, customers' pipes, and manholes are watertight. We do this by: 

• Relining sewers in the most affected areas to stops water from getting into our pipes, improving our network without impacting customers too much.
• Building new wetlands across the county, these will soak up excess rainwater, helping to prevent groundwater flooding.
• Ensuring our customer's pipes are watertight using a technology called Tubogel. This helps to seal any gaps in private pipework, preventing groundwater from getting into the network.

Extreme weather is becoming increasingly common and groundwater issues are too. But we’re investing in solutions to protect our customers for years to come.