The Tamar in a Changing Future

What Will the Tamar Look Like in 2040?

What the official 2025 sewage data tells us about the system we are relying upon for the future

When we talk about sewage in the River Tamar, it is easy to become lost in numbers: spills, hours, overflows, rainfall and investment programmes stretching decades into the future.

So Drip Drip decided to look closer to home.

One of our volunteers, Martin, went through South West Water’s 2025 Event Duration Monitoring (EDM) annual return and extracted the figures for storm overflows relevant to our stretch of the Tamar.

What emerged deserves attention.

What happened in 2025?

At Harewood Road in Calstock, the storm overflow recorded 164 counted spills during 2025, totalling 1,029 hours of discharge.

That amounts to more than six weeks of accumulated discharge time over the course of the year.

And Harewood Road is not an isolated example.

Metherell WWTW storm tank recorded 118 spills totalling 2,299 hours.

St Dominick WWTW recorded 93 spills and 1,669 hours.

St Dominick Pumping Station recorded 72 spills and 1,067 hours.

Gunnislake WWTW storm tank recorded 94 spills and 956 hours.

Harrowbarrow WWTW recorded 68 spills and 628 hours.

These figures should not simply be added together: several overflows can operate at the same time. Nor do they tell us the volume of sewage discharged.

But they do tell us how extensively parts of the local wastewater system relied upon storm overflows during 2025.

Four words that caught our attention

There is something else in the annual return which may be even more revealing than the spill numbers themselves.

Water companies are required to identify reasons for high spill frequencies.

Against Harewood Road, South West Water records:

“Not asset maintenance – hydraulic capacity.”

In ordinary language: lack of capacity.

And Harewood Road is not alone. The same explanation appears against a number of assets in the local data.

That matters.

Drip Drip does not have to speculate that parts of the wastewater system are struggling with capacity. South West Water’s own regulatory return identifies hydraulic capacity as the reason for high spill frequency at these locations.

Elsewhere, the reasons differ. At Metherell, for example, the return identifies surface-water infiltration — another way in which rainfall can place pressure upon a wastewater system.

What does a “spill” actually mean?

We need to be careful with these figures.

The Environment Agency uses what is known as the 12/24-hour counting method. A “spill” in the annual return is therefore a regulatory measure and is not necessarily the same as counting every occasion on which an overflow starts discharging.

EDM monitors record when an overflow operates and for how long. They do not measure the volume discharged.

So the 1,029 hours recorded at Harewood Road should not be described as 43 continuous days of sewage. It means that, added together, the monitor recorded 1,029 hours of discharge during 2025.

We think those distinctions matter.

If we are going to challenge the performance of our wastewater infrastructure, we should be as careful with the evidence as we expect the water industry to be.

And 2025 was relatively dry

There is another reason these figures caught our attention.

Across large parts of England, 2025 was significantly drier than 2024. Nationally, the number of monitored storm-overflow spills fell by 35%, while total spill duration fell by 48%.

The Environment Agency itself says much of that reduction reflected the unusually dry conditions and that storm-overflow activity is strongly linked to rainfall.

Yet individual assets around our stretch of the Tamar still recorded hundreds — and in some cases more than a thousand — hours of discharge.

Which raises a much bigger question.

What happens as the world around the system changes?

South West Water has investment plans. It has plans for climate resilience. Major improvements are promised, some stretching towards 2040 and beyond.

We welcome investment that genuinely improves the health of the Tamar.

But the wastewater system of 2040 will not be operating in the world of 2025.

Climate breakdown is expected to bring increasing pressure from extreme weather. More intense rainfall and flooding present obvious challenges for drainage and wastewater infrastructure, while drought and heat place different pressures upon the river itself.

And climate is not the only change.

Our communities need homes, including genuinely affordable homes for local people. But new development also brings additional demand for sewerage and wastewater treatment.

Calstock Parish’s current Neighbourhood Development Plan runs to 2030. Whatever development follows must surely be matched by the infrastructure needed to support it.

This is not an argument against new homes. It is an argument for infrastructure before — or at the very least alongside — development.

So the wastewater system of 2040 may have to serve growing communities while simultaneously coping with a more challenging climate — even though parts of today’s system are already experiencing capacity problems.

Are we planning the wastewater system the Tamar catchment will actually need — or improving the system we needed yesterday?

2040 is somebody’s future

This is why dates such as 2040 matter.

They can sound comfortably distant when written into an investment programme. But 2040 is not simply a date on a spreadsheet.

Today’s children will be adults.

Others who will live beside, depend upon and perhaps fight for this river have not yet been born.

Those of us campaigning for the Tamar today will grow older. Some of us will no longer be here. Companies will change, governments will change and investment programmes will be replaced by new ones.

But the river will remain.

The decisions being made now will help determine the Tamar those generations inherit.

Who speaks for the river then?

This is one reason Drip Drip is working towards a Charter for the River Tamar and recognition of Rights of the River.

River Rights are about looking beyond our own timescales.

They ask us to consider the health of the river not simply as something to be balanced against today's priorities, but as an interest that deserves a continuing voice of its own.

A voice for the Tamar when ours fade.

And, in doing so, a voice for generations who cannot yet speak for themselves.

The 2025 sewage data tells us what happened last year.

The more important question is what we choose to do with that knowledge now.

Because 2040 is not the end of an investment programme.

It is the beginning of somebody else’s inheritance.

About the data

The figures in this article come from the Environment Agency’s 2025 Event Duration Monitoring Storm Overflow Annual Return, using data supplied by South West Water.

EDM records when storm overflows discharge and the duration of those discharges. Spill counts use the Environment Agency’s 12/24-hour counting methodology. EDM does not measure the volume discharged, and discharge hours from different overflows should not simply be added together because overflows may operate simultaneously.

Our local data was extracted and collated from the annual return by a Drip Drip volunteer, Martin Smith, whose work enabled us to examine what the national dataset means for our own stretch of the Tamar.

Drip Drip – Friends of the River Tamar