Why water decides what you can do with land

Drainage is one of those things that rarely appears in the estate agent's particulars, yet it shapes almost everything you will want to do with a smallholding. A field that only carries stock from May to September is worth a great deal less than one that grazes through the winter, and no amount of good fencing or a new shed will change that. Wet ground poaches under hooves, turns gateways into bogs, and rules out machinery access just when you need it most.

It also affects what you can build. Planning authorities will want to see how foul drainage and surface water will be dealt with, and a soakaway or drainage field needs ground that actually accepts water. If the water table sits a spade's depth below the surface in February, that conversation gets difficult very quickly. So before you fall in love with a view, spend a day finding out where the water goes.

Time your visit for wet weather

Summer viewings flatter almost any piece of land. Free-draining loam and heavy clay can look remarkably similar in August. If you possibly can, go back between November and March, ideally 24 to 48 hours after a decent spell of rain. That is when the truth shows itself: standing water in the hollows, ruts holding puddles, dark damp patches that never seem to dry.

Take wellington boots, a spade, a notebook and your phone for photographs. Walk the whole boundary rather than the footpath, and pay attention to the low corners, the gateway sills and the shaded side of hedges, which dry out last. If the vendor is reluctant to arrange a winter visit, that in itself is worth noting.

Walk the boundaries: ditches, culverts and outfalls

Start at the lowest point of the land and work uphill. Water always tells you its story from the bottom. A ditch is only as good as its outfall, so follow it until you find where it discharges, whether into a stream, a culvert under a lane, or a neighbour's ditch. If the outfall is higher than the ditch bed, the whole system is effectively dead and no amount of clearing will fix it.

• Look for silt: a ditch should have a defined channel. If it is a shallow grassy trough, it has not been cleaned in years.
• Check culvert inlets: lift debris and look inside with a torch. A blocked or half-collapsed pipe is a common and expensive surprise.
• Assess the outfall level: a tape measure and a level will tell you whether water can physically leave the site.
• Note the vegetation: rushes, sedges, creeping buttercup and tufted hairgrass all point to ground that stays wet for much of the year.
• Check the neighbours: land uphill that has been drained, built on or compacted may now send more water your way.

Dig a hole and read the soil

This is the step most buyers skip, and it is the most revealing. Dig a pit about 60cm deep in several places: the highest corner, the lowest corner, mid-slope and near any suspected wet patch. Look closely at the subsoil as you go down, and note the depth at which it changes.

Orange and rusty flecks mixed with grey patches, known as mottling, mean the soil is periodically waterlogged: water sits, then drains away. A solid grey-blue layer with a faint sulphurous smell means it is wet almost all the time. Both can be worked with, but they need different solutions and different budgets. Roll a handful of subsoil between your palms; if it forms a long, sticky ribbon, you are dealing with clay, which drains slowly and compacts easily.

Slope, springs and what lies uphill

Water does not respect boundaries. A gentle fall across a field is a good sign, but look for seepage lines where springs break out at the base of a slope or where a band of clay meets free-draining ground. These often show up as ribbons of rushes or a strip of ground that never firms up.

Then look up and out. Is there a road, a yard, a new housing development or a heavily stocked field above you? All of these can shed water onto your land. Ask the vendor whether there have ever been problems, and ask the neighbours too, politely and separately. Local knowledge about a field that "always floods by the bottom gate" is worth more than any map.

Weighing the cost of putting it right

Some drainage problems are cheap. Clearing a silted ditch, rodding a culvert or reinstating a few metres of field drain might cost a few hundred pounds and a weekend. Others are not: a flat clay field with no fall and no functioning outfall may never drain properly, whatever you spend.

Ask for any existing drainage plans or old map references showing field drains. If the land is worth pursuing, get a contractor to quote for the work before you exchange, and use that figure in your offer. Remember that works on an ordinary watercourse usually need land drainage consent, and that ditches on your boundary come with riparian responsibilities. If the numbers do not stack up, or if the only fix would involve a neighbour's cooperation you cannot guarantee, be prepared to walk away. There is always another field.