A well-built garden path should be invisible in the worst weather. You shouldn't be thinking about it at all — you should be walking to the shed in the rain, mug in hand, without wondering whether the third slab will squirt muddy water up your trouser leg. Unfortunately, most paths are laid in that first optimistic week of summer, when the ground is dry and drainage feels like a theoretical problem. Then October arrives, and the route from the back door to the bin store turns into a shallow brook that leaves a tidemark of grit across the patio.

The good news is that water is predictable. It runs downhill, it takes the easiest route, and it will find any weak point in your construction. Design for it deliberately and you'll have a path that still looks tidy in February.

Start With the Slope, Not the Slabs

Every decision about a path flows from its fall — the technical term for the gentle gradient that moves water along. For most domestic paths, you want a crossfall of about 1:60 to 1:40, which means the surface drops roughly 15 to 25mm across every metre of width. That's shallow enough to be comfortable underfoot and walkable for anyone unsteady on their feet, but steep enough that water never sits.

Where you have the luxury of space, run the fall sideways into a planting bed or gravel margin. Where the path sits between two walls or fences, you'll need a fall along the length instead, ending in a soakaway, a drainage channel or a lawn. What you must avoid is a flat path, or worse, a path that dips in the middle. Standing water is the enemy of every jointing material, and a puddle that sits for three days will lift mortar, loosen sand and turn sub-base into porridge.

Check levels with a string line and a spirit level before you dig. It takes twenty minutes and saves weekends.

Choose Surfaces That Let Water Through

Traditional paving is impermeable by nature, which is why so many garden paths behave like small rivers. The fix is to either let water through the surface or capture it at the edges.

• Permeable block paving uses wider joints and an open-graded sub-base, so rain drains between the blocks rather than across them.
• Resin-bound gravel gives a smooth, firm finish that water passes through easily — ideal for wheelchair and pushchair access.
• Loose gravel over a geotextile membrane is cheap, quick and excellent at absorbing rainfall, though it needs raking and topping up annually.
• Stepping stones set into gravel or grass are the most forgiving option of all, because the majority of the surface is ground that drains naturally.
• Bark or woodchip suits informal kitchen-garden routes, but expect to replace it every couple of years as it breaks down.

If you're laying impermeable slabs anyway — perhaps for a formal look — build in a fall and put a gravel-filled drainage strip alongside. A 100mm wide channel filled with 10mm pea gravel, running the length of the path, will take far more water than most people expect.

Build a Sub-Base That Won't Shift

Drainage starts below the surface. A path laid straight onto soil will rut, sag and hold water within a season. Excavate to at least 100mm for pedestrian routes and 150mm where a wheelbarrow or mower will travel, then compact a layer of MOT Type 1 or a similar crushed stone sub-base in two passes.

On heavy clay — which covers a good deal of the UK — dig deeper and add a 50mm layer of coarse gravel beneath the sub-base as a drainage blanket. Clay holds water like a basin, so any path over it needs somewhere for that water to go before the slabs go down. Line the excavation with a permeable geotextile to stop fines migrating upwards and clogging your drainage stone.

Falls should be built into the sub-base, not just the surface. If your sub-base is level and your slabs slope, you're relying on the mortar bed to make up the difference, and it will fail.

Use Gravel Margins as a Safety Valve

The simplest drainage upgrade to any existing path is a gravel margin along one or both sides. A strip 100–150mm wide, dug to about 75mm deep and filled with washed gravel, acts as a sponge and a soakaway combined. Water that sheets off the paving falls into it, percolates down and disappears, rather than running along the edge and washing soil onto the surface.

Margins also protect the path's edges from crumbling, hide the slightly ragged line where paving meets soil, and give you somewhere to plant low thymes, alpine strawberries or sedums that will tolerate occasional wet feet. On slopes, add a short length of perforated pipe in the gravel at the lowest point, directed towards a border or soakaway.

Don't Forget the Joints and Edges

Water gets in through the smallest gap and does its damage from below. Brush kiln-dried sand into block paving joints once they're dry and top it up each spring — this alone prevents a great deal of movement. For rigid paving, use a mortar or resin joint that's rated for external use, and never leave a joint hollow.

Edging matters more than most people realise. Restrained edges — set in concrete or pinned with steel — stop the path spreading and keep the fall consistent. An unrestrained edge will splay within two winters, and once the fall is lost, the puddles begin.

Finally, keep the path clear. Sweep leaves in autumn, pull weeds from gravel margins before they root deeply, and check that any channel or gully at the bottom of the run isn't silted up. A path that drains well is mostly a path that's been given a little attention at the right moments. Get the levels and materials right at the start, and the rest is simply maintenance — the easy kind, done in a jumper rather than a wetsuit.