Choosing a pump for a small garden water feature

Start with flow, not wattage

Every pump in a British garden centre is rated in litres per hour (lph), and it is tempting to buy the biggest number you can afford on the theory that more is better. In a small feature it rarely is. A half barrel with a spout that throws water 600mm into the air will empty itself over the rim in a stiff breeze, and a bubble fountain turned up too high sounds like a kettle coming to the boil.

As a rough starting point for a small garden feature: a gentle bubbler or single spout in a container wants 150–400 lph; a millstone, pebble pool or small bowl wants 400–800 lph; a short rill or a 200mm cascade wants 600–1,200 lph. A wildlife pond is a different animal altogether — you are not moving water to feed a filter, so the goal is barely any movement at all, and often no pump is the kindest choice.

Whatever you buy, pay the extra few pounds for a model with a flow control valve, or fit an inline valve on the hose. Being able to throttle a pump back by half is the single most useful feature on a small water feature, because you can tune the sound and the splash without buying a second pump.

Working out head height

Head is the total vertical distance the pump has to lift water, measured from the surface of the water — not the bottom of the pond — to the highest point the water reaches. If your barrel has 300mm of water in it and the spout sits 250mm above the rim, that is roughly 0.55m of head, not the full depth of the container.

Then add a little for friction. Every metre of flexible hose, and every sharp bend or elbow, adds roughly 0.1–0.2m of equivalent head. A pump in a barrel with 2m of hose and a couple of bends is realistically working against 0.8–0.9m.

Crucially, look at the pump's performance curve rather than just its maximum head figure. A pump rated at 1.2m maximum head delivers almost nothing at 1.2m; it might manage 700 lph at 0.2m and 300 lph at 0.6m. A good rule of thumb is to choose a pump whose maximum head is about 1.5 times your calculated head, so it sits comfortably in the middle of its range rather than gasping at the top of it.

What the running costs really look like

Small submersible pumps usually draw between 5W and 30W, and the difference matters because most of us run them continuously through the growing season, and many of us run them all year.

• A 5W pump running 24 hours a day costs roughly £13 a year at around 30p per kilowatt hour.
• A 20W pump costs about £50 a year on the same basis.
• A 60W pump — far too big for a half barrel — would cost around £160.

So a modest upgrade in efficiency pays for itself quickly. Look for the wattage on the box rather than the "equivalent" marketing numbers, and consider a solar pump for a small bubbler in a sunny corner: it costs nothing to run and switches itself off at dusk, which suits a quiet garden. The trade-off is that output drops on cloudy days.

Matching the pump to the feature

• Container, half barrel or glazed pot: a compact 5–15W submersible with integral flow control, sized for 200–400 lph at your working head.
• Bubble fountain or small sphere: 300–600 lph, with the outlet just clear of the water so the bubbles break cleanly.
• Millstone or pebble pool: 500–900 lph, spread across the stone so the water sheets rather than jets.
• Short rill or small cascade: 700–1,200 lph, and check the channel is level or the water will run down one side.
• Wildlife pond: no pump, or a very low-flow one raised on a stone so it disturbs only the surface. Frogs and newts prefer still water.
• Small fish pond: aim to turn the volume over every two to four hours, and choose a solids-handling pump if there is any sludge or blanket weed.

Maintenance: the bit that decides whether you enjoy it

A pump you cannot clean easily will be a pump you resent. Before you buy, look at how the impeller is accessed and how the intake is protected.

• A removable rotor or impeller that comes out without tools, so you can clear grit and hair in a couple of minutes.
• A foam pre-filter that can be lifted out and rinsed in a bucket of pond water — never under the tap, which kills the bacteria living in it.
• An intake grille with holes big enough not to clog with blanket weed every fortnight.
• A decent length of cable, and a low-voltage option where children or pets have access to the water.

Stand the pump on a brick, slate or purpose-made plinth so it is not sitting in silt, and keep it away from the sides of the container to cut down on vibration. Even a good pump hums if it is touching the wall of a barrel.

Winter, noise and a last check

In most of the UK a small pump can run through winter, provided the outlet never freezes — if ice blocks the spout, the pump keeps pushing and can burn out. In a hard frost, either lift the pump out, clean it and store it in a bucket of water in the shed, or leave it running just below the surface. Never let a pump freeze solid with water inside it.

On noise: rubber feet, a solid base and a little distance from the container wall make more difference than the price tag. And before you commit, check the cable route — you want it hidden, protected and running to an outdoor socket on an RCD. Get those two things right and the pump will quietly disappear into the background, which is exactly what you want from the heart of a small water feature.