My host sister and I rode bicycles to Maejo University past backyard boarding houses (one-room bungalows with thatched roofs), fields of all kinds of vegetables, grazing water buffalo and bony cows, little shops, homes-- a mish-mosh of land uses. The whole way we dodged manholes that lead to a ditch. After a bit of sleuthing I figured out that this ditch is where we toss our dirty water, full of detergent and fabric softener, after washing clothes by hand in these big basins. I assume everyone else in the neighborhood does the same, plus some people probably have their sewage piped there. This ditch follows the road until the road starts to curve, then empties into a big rice paddy. So the water full of chemicals, raw sewage, and oily runoff is being used to grow the rice. If only plants had some sort of biological mechanism for filtering that stuff out before sucking it up via transpiration.