|Rainwater is collected in a large urn by a family's open kitchen in Isaan|
You're bound to see them most anywhere in the kingdom of Thailand, in settings as varied as the styles of the containers themselves. From the simplest 55 gallon/190 liter plastic drums to bulbous cement or pottery urns to 250 gallon/1,000+ liter plastic drums and huge commercial stainless steel cylindrical containers like you'd see on the rooftops of stores or hotels in more urban areas.
In the countryside you're likely to see pottery-style urns such as the one above, with a trough slanted down from the roof that collects rainwater during the wet months. These are some of the most common for folks who don't want to use the plastic containers (or the stainless steel ones, which can develop tiny leaks within a few years).
Most of you know that rainwater is "soft" water, free from the calcium, lead and magnesium that can come from treated water. You can, however, still get contaminates from whatever washes off of your rooftop into the containers, but given the choice I'd still go with rainwater, even if only for bathing. Cooking with it and drinking it are another story. Legionella (remember Legionaire's disease in the news some years back?) and other risks are always there, I suppose, but there are filters and means of avoiding that which we don't need to go into here today.
Nevertheless, you'll see them almost everywhere... and why not? It's free water and fits hand-in-glove with the Thai way of conserving resources and costs. Waste not, want not.
Over the years I've seen more types of collection/storage containment devices than I'd have fingers - even if I resembled a the multi-handed Hindu-style statue. It was an idea I happily borrowed; after my first visit I set up a few 55 gallon drums and had my rain gutters empty into them, saving the water for watering the yard after the rains had stopped.
Naturally, standing water is a prime breeding ground for mosquitoes - something else you're sure to see (and perhaps suffer from) in Thailand, but a few mosquito fish (Gambusia affinis) will keep them under control. Many county health departments will provide them for free, if you contact them and ask. Just a few in your garden containers will do the trick.
One trip I took a few pictures of tanks on the roof of a school building. There were some tanks with the lids askew (like the one below), and I wondered if it was intentional (unlikely) or merely what I like to call "the curse of the lowest bidder" when the service company was hired (much more likely).
Friends who've grown up on farms have told me that when they had a true, down-into-the-ground well that they had to draw or pump from there were often unfortunate snakes, frogs, rodents and the likes down in them. I suspect that gave the water it's own "zing" that didn't fall under the heading of piquant, but I suppose they got used to it. I also suppose there are similar visitors to these water-gathering containers, via one opening or another.
Naturally, rain barrels aren't in use in different forms in many other countries, but I enjoy details like these wherever I go... and now you know a bit about the "barrels" in Thailand.