I’ve been thinking about ways to get a minimal-impact hosepipe going at Kate’s allotment. At present she has a reservoir in a water-butt that collects off the shed roof, and she dips a watering-can in there to pour on the veg patch. I figured if you could lift the water to say the height of the shed roof, it would be enough to simply siphon off water with a hose that would allow the whole allotment to be watered without returning to the reservoir. I figured the pump technology wouldn’t have to be very advanced, since it would have all day to pump the water up to the header tank.

Mark at work suggested a sealed tank with a hose trailing in the reservoir: as the sun heats it during the day, the air within expands, and bubbles out of the end of the hose. At night, as it contracts, it draws water up the hose into the higher tank. To draw off water, you would open a tap at the bottom of the tank and take the hose out of the reservoir.

I did some calculations. Using a daytime max. temperature of 10 celsius and night time minimum of 5 celsius, and an 80-litre bin, this machine would suck 1.5 litres a day to a maximum height of 1.7 metres.

I imagine Kate’s in the habit of pouring slightly more than that on her cabbages.