Read the slope before you lift a spade

A sloping garden is a gift for a water gardener. Gravity does the work, and the fall lets you create riffles, pools and a burbling sound. Before you reach for a spade, spend time reading the slope. Watch where rain already runs during a downpour. That natural pathway is often the best line for a brook, because it follows the land rather than fighting it. Check the fall with a string line and spirit level: a drop of 100mm over 5 metres is gentle; 300mm or more over that distance gives stronger flow and more scope for small cascades. Note the soil. Clay holds water well but can be slick and unstable. Chalk and limestone drain quickly and may need a good liner. Sandy soil is easy to dig but needs firm edges. Look for tree roots and buried services before digging, and think about where surplus water will go. A small soakaway or a gentle overflow into a planted bog area is far better than a flooded neighbour's garden.

Plan a meandering line with pools and riffles

Natural brooks rarely run straight. They curve around obstacles, widen into pools and narrow into shallow riffles. Lay out a hosepipe or length of rope in a gentle S-curve, then stand back and look at it from an upstairs window. Avoid sharp bends and perfect symmetry. A brook 40–60cm wide is easy to manage; let it widen to 1–1.5 metres at pools. Depths should vary, too. Shallow riffles of 5–10cm keep the water moving and oxygenated, while pools of 30–45cm give wildlife somewhere to shelter. Place pools on the outside of bends and riffles on the straighter sections. If you want a still pool at the bottom, make sure its edges are level. A flexible butyl or EPDM liner is the practical choice for a sloping brook; it allows you to fold and shape the channel. Add a geotextile underlay to protect it from stones and roots. Allow 30cm of liner beyond every edge, and more where the slope is steep.

Build the bed with liner, local stone and gravel

Excavate in stages, starting at the top and working down. Create shallow shelves along the sides for planting and for wildlife to climb out. Line the channel, folding the liner neatly at bends. Don't worry about perfect creases; they will be hidden. Now comes the stone. Local stone is best: sandstone, limestone or granite, depending on where you garden. It will look at home immediately and weather naturally. Use larger stones to edge the brook, form small weirs and create planting pockets. Washed river gravel or pea gravel, 10–20mm, is ideal for the bed. A layer 3–5cm deep gives the look of a natural stream and protects the liner. Avoid sharp, angular gravel that can puncture. Build weirs by placing a flat stone across the channel with a slight fall. Water should glide over, not crash. Hide the liner edges with turf, stones or creeping plants. If you are using a pump, put it in a sump at the lowest point: a buried crate or bucket, covered with gravel and accessible for cleaning. Run the hose up the slope, bury it, and disguise the outlet with stones. A low-voltage pump moving 2,000–4,000 litres an hour is plenty for a brook. Aim for a gentle flow, not a torrent.

Plant for cover, colour and clean water

Planting is what makes a brook look established rather than newly built. It also shades the water, filters nutrients and gives wildlife cover. Choose British natives where you can.

• Shallows: marsh marigold, water mint, water forget-me-not, lesser spearwort and flag iris.
• Boggy edges: ragged robin, meadowsweet, purple loosestrife and soft rush.
• Shade: ferns and hostas.

Add oxygenators such as hornwort or water crowfoot. Plant in aquatic baskets lined with hessian and filled with loam, then top with gravel to stop soil washing away. Avoid invasive plants: parrot's feather, floating pennywort, water fern and Himalayan balsam are all trouble in UK waterways. Leave some open water for birds and dragonflies, and create a shallow beach at one end so hedgehogs, frogs and thirsty birds can drink safely. A few flat stones at the water's edge give amphibians an easy way out.

Manage flow, top-ups and wildlife year-round

Once running, a brook needs only gentle care. Top up with rainwater from a water butt rather than tap water, which contains chlorine and nutrients that encourage algae. In autumn, skim or net fallen leaves before they sink and rot; a build-up of leaf litter will clog the pump and cloud the water. Check the pump intake regularly and clean it. In winter, moving water usually resists freezing, but if ice forms, do not smash it—trapped gases can harm wildlife. Place a floating ball or a pan of hot water on the surface to create a breathing hole. In spring, divide overcrowded plants and remove any dead growth. Watch for leaks: a sudden drop in water level is not evaporation. Liner repairs are straightforward with a patch kit. Resist the urge to stock fish in a small brook; they eat frogspawn and tadpoles. Let frogs, newts, damselflies and birds arrive in their own time. Keep fertilisers and pesticides well away from the water, and never use them on the banks. A natural-looking brook is never finished. It shifts, silts and grows, and that is part of its charm. Sit back, listen to the water, and enjoy the wildlife that finds it.