I have yet to live in a house in Thailand that has had guttering and downpipes, but am planning on installing them, as it will prevent rain from blowing back onto exterior walls and also water splashing up from the ground. All the channelled rainwater will then go into the pond next to my house.

I had considered putting in tanks, but the issue is that the first part of the downpour will wash off all the crap from your roof into your tanks and that grit will erode your pumps if not filtered out. You could install a valve to divert the initial flow of dirty water, but short of actually remembering to run out into the rain after 15 minutes to switch the valve to the collecting tanks, I have yet to see any solution.

I guess you could have a settling tank installed prior to being siphoned off into the 'clean' tank before pumping, but this seems to turn a simple collection exercise into a water engineering project, plus maintenance would be a pita.

I'll be interested in hearing of an easy solution too.