I'm at work, waiting for a meeting, so I had 5 mins to draw this, using Paint:
raincollector.jpg

It's a "technology" first used at the monastery and that the neighbouring houses are copying. Because the climate is prone to heavy showers and long droughts, and the ground doesn't hold moisture very well (it all seeps down to the river), the collection of rainwater into reservoirs is a plus for households.
That's why "everybody" is doing it around here.
(I'm not being original, the collection of rainwater into reservoirs (sometimes underground, often shaded) is very important for cities with this kind of climate - I'm thinking both Angkor in Cambodia and any Maya city in the Mexico riviera.