A few thoughts for your research.

Firstly - it's very confusing as to what you're actually after. I think you're after the potential for solar lights or solar water features. In which case, don't you want to know the total usage of these features, irrespective of whether the gardener is in the garden at the time?

secondly, you could do with a little more time considering your target audience for this questionnaire. Most people on uk.rec. gardening are keen gardeners - we spend a lot more time growing plants that we do lounging around admiring our water features. So compared with the UK garden-using population, we're a pretty biased sample!

And that bring me to the third point - if you'd read the information on gardenbanter, you would see that it is merely a portal for usenet - ie it forwards posts, in this case, to the newsgroup uk.rec.gardening and retrieves answers from that group. Most of the people who would be likely to answer your questionnaire are posting directly to e.rec.gardening - they won't even see your poll! (Yes, I know you've given the url, but people won't come across from urg and register with gardenbanter just to add to your poll._