There are four common causes and they look the same from the back door: compacted soil, heavy clay, a low spot with nowhere to drain, and water being shed onto the garden from a hard surface or a downpipe. Compaction is fixable cheaply; a genuine drainage problem needs a land drain to a soakaway. Diagnose before digging.
- Compaction is the most common cause and the cheapest to fix. Test for it first.
- A soakaway only works if the ground beneath it actually drains. On clay, often it does not.
- Check where your downpipes discharge before blaming the soil.
- Never solve your drainage by sending water to a neighbour. It is their problem and then your dispute.
Four causes that look identical
| Cause | How to spot it | What fixes it |
|---|---|---|
| Compaction | Water sits in a thin layer; spade is hard to push in | Aeration, organic matter; sometimes mechanical |
| Heavy clay subsoil | Clay visible a spit down; sticky, holds its shape | Improve topsoil; land drain if severe |
| Low spot / wrong levels | Water pools in one defined area | Regrade, or drain that point |
| Run-off from hard surfaces | Floods after rain, near paving or a downpipe | Redirect or intercept the run-off |
| High water table | Wet even without recent rain; water in a test hole | Raised beds; drainage is limited help |
| Blocked or broken drainage | Gully overflowing, or a wet patch over a drain run | Clear or repair the drain |
The last two are less common and worth ruling in or out early, because the remedies are quite different. A high water table in particular cannot be drained away — there is nowhere for the water to go.
Test before you spend
Two simple tests separate most of these, and both are free.
The spade test, for compaction
Push a spade into the lawn. If it goes in easily to its full depth, the soil structure is reasonable. If it stops a few inches down and needs real force, you have a compacted layer — often a pan just below the surface, common on gardens laid by builders who rolled topsoil over compacted subsoil. That pan is why water sits on top rather than soaking away, and it is fixable.
The percolation test, for drainage
Dig a hole roughly 300mm square and 300mm deep. Fill it with water and let it drain completely. Fill it again and time how long it takes to empty. Under four hours is reasonable drainage. Four to twelve hours is slow but workable. Over twelve hours, or if it is still holding water the next day, the ground is not draining and a soakaway will not work there.
That second test matters more than anything else on this page, because it tells you whether the standard solution — drains to a soakaway — is even viable on your plot.
Compaction: the common and cheap one
This is the cause we find most often, and it is routinely misdiagnosed as a drainage problem requiring excavation.
Compacted soil has had the air squeezed out of it. Water cannot move down through it, so it sits on the surface. Grass roots cannot get down either, which is why a compacted lawn is also usually thin and mossy.
It is extremely common on newer housing, where topsoil was spread over a subsoil compacted by construction traffic, and on any lawn that takes heavy use in winter.
The fixes, in order of intervention: hollow-tine aeration, which removes cores and lets air and water in; top dressing with sharp sand and compost brushed into the holes; and, for a severe pan, mechanical decompaction which fractures the layer without turning the surface over.
Done properly, a compacted lawn that puddled all winter can drain acceptably the following year. It costs a fraction of installing drainage, and it is always worth trying first where the percolation test shows the ground beneath will actually accept water.
When you genuinely need drainage
Where the percolation test is poor and the problem is persistent, the standard answer is a land drain system: perforated pipe laid in gravel-filled trenches, falling to a soakaway or, where permitted, a surface water connection.
Three things decide whether it works.
Where the water goes. A soakaway disperses water into the surrounding ground, so it only works if that ground drains. On heavy clay a soakaway can simply become an underground pond. In that case the options are a connection to a surface water sewer, where one exists and the water authority permits it, or a different strategy entirely.
Sizing and siting. A soakaway must be sized for the area it serves and sited a sensible distance from buildings — too close and you are introducing water next to foundations.
Falls. Land drains work by gravity. On a flat plot there may be nowhere for the water to fall to, which is a real constraint rather than a detail.
Where none of that works, raised beds and planting chosen for wet ground is a legitimate answer. Some gardens cannot be drained, and designing around the water is better than spending on a system that will not perform.
Check the easy things first
- Where do your downpipes discharge? A downpipe emptying onto the lawn rather than into a gully puts a roof's worth of water into one spot. Astonishingly common, and trivially fixed.
- Is the gully blocked? A blocked gully makes a perfect downpipe useless and backs water up at the base of the wall.
- Does a hard surface drain towards the garden? A patio or drive with the fall running the wrong way delivers its run-off to the lowest point of the lawn.
- Has a neighbour changed their levels or surfacing? Water arriving from next door is a real and increasingly common cause.
- Is there a spring or a ditch nearby? Worth knowing before designing anything.
- Was the garden recently built on or dug up? Construction traffic compacts ground severely.
Do not send it next door
Worth stating plainly, because it is the shortcut that creates disputes.
Water you drain from your land becoming a problem on a neighbour's land is not a solution. It can be a legal liability, and it is reliably the start of a bad relationship.
That applies to grading a garden so it falls towards a boundary, to discharging a soakaway too close to a boundary, and to laying a hard surface that sheds its run-off next door.
The correct approach is to deal with the water within your own boundary — a soakaway sized and sited properly, a permeable surface, or a connection to drainage where one is available and permitted. If the only workable answer involves the neighbour, that is a conversation to have in advance rather than a fact for them to discover.
What it costs
These are the landscaping figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Landscaper, hourly | £15–£40/hr | Task dependent |
| Day rate | £150–£250/day | Per landscaper |
| Patio | £80–£150 per m² | Material dependent |
| Block-paved driveway | £80–£120 per m² | Excavation extra |
Drainage is priced per job because the variables are the depth, the length of run and whether a soakaway is viable. Aeration and top dressing sit at the cheaper end, and are worth trying first wherever the percolation test allows.
We dig a test hole before quoting, because on some plots a soakaway simply will not work and it is better to know first.
Frequently asked questions
Why does my garden flood when it rains?
Most commonly compacted soil, which stops water moving down so it sits on the surface. Other causes are heavy clay subsoil, a low spot with nowhere to drain, and run-off arriving from a hard surface or a downpipe. They look identical from the back door and need different work, so test before spending.
How do I know if my soil is compacted?
Push a spade into the lawn. If it goes in easily to full depth the structure is reasonable; if it stops a few inches down and needs real force, there is a compacted pan. It is very common on newer housing where topsoil was spread over subsoil compacted by construction traffic.
Will a soakaway fix my waterlogged garden?
Only if the ground around it actually drains. Dig a 300mm test hole, fill it twice and time how long the second filling takes to empty. Over twelve hours, or still holding water next day, means a soakaway will become an underground pond. On heavy clay that is a common finding.
Can I just aerate the lawn?
Often yes, and it is always worth trying first where the ground beneath will accept water. Hollow-tine aeration plus top dressing with sharp sand and compost transforms many lawns that puddled all winter, at a fraction of the cost of installing drainage. For a severe pan, mechanical decompaction goes further.
Where should my downpipes discharge?
Into a gully connected to the drainage system, not onto the lawn or the ground beside the wall. A downpipe emptying onto a lawn delivers a roof's worth of water into one spot, and it is a surprisingly common cause of a wet garden. Check the gully is clear and actually connected while you are there.
Can I drain water towards my neighbour?
No. Water you drain from your land becoming a problem on a neighbour's can be a legal liability and reliably causes disputes. Deal with it within your own boundary — a properly sized and sited soakaway, a permeable surface, or a permitted drainage connection. If the only answer involves them, discuss it first.
Test before you dig
A spade and a test hole tell you whether this is compaction or drainage, and that decides whether you spend hundreds or thousands. We do both before quoting.