[Kate-in-Roquebrun]

Any advice please about the size of watertank needed for a new, hot, dry garden (in Languedoc). I'm not anticipating a lawn, obviously, and will have as much drought-resistant planting as possible, but hope to grow vegetables and will also have plants in containers. The cistern will be underground so its size will affect the building costs. 1000 litres sounds large (about 5 times the size of my water butt in London), but would this be too small in a hot dry summer? 

[John J]

Kate, a lot depends on the size of your garden. I can only go by my own experience. I connected a 700 litre water tank to collect rainwater from the roof of our double garage. I found that one or two good, heavy downpours filled it so I linked a second one to it, making 1,400 litre capacity. As there was little need to use the water for irrigation during the winter once they were full the excess overflowed into the ground. When I did begin to use them they emptied very quickly. When you consider that 1,000 litres will only fill a 10 litre watering-can 100 times you can work out roughly how long it will last.

[Alice]

It would depend on many factors, Kate: size of plot, number of plants, how windy/shady your plot is, annual rainfall etc, but in my opinion a 1000 litre tank (one cubic metre) is way too small. You would need to give 20 litres per plant (deep watering) every 2-3 weeks over the summer months unless there is rain. Vegetables are thirsty and would require frequent, possibly daily watering. You could wean trees/shrubs off water after a while, depending on your conditions, but even some of these will require the occasional soak. We have a 30 cubic cistern and it is certainly not enough (however, we do have 600+ plants). With our annual precipitation of 350mm, it gets filled from roof run-off during the winter months, so a 1-cubic tank will fill up very quickly and most of the rest of the water will be wasted. There is no comparison with London conditions. We rarely use all the water from our water butt in London.
I would suggest you have the biggest cistern you can afford. You will not regret it.

[Alisdair]

We have a 16 cu metre cistern in Greece (where we do have a mains water supply for topping up) and though we are very rarely there in summer, and try to keep most of the garden unwatered, it's only just about adequate then, which is when the public water supply is least reliable. So I'd strongly support Alice's Go Big advice!

[Kate-in-Roquebrun]

Thanks to everyone for your useful advice. I'm very glad I asked!

[David Bracey]

You cannnot have enough water even in the Languedoc.