I have never been to Asia, but if I was going there I would probably bring either a 1 oz bottle of chlorine bleach (a couple drops per liter, wait half an hour) or a Steripen, or maybe both. Small and light, I would consider carrying that as an insurance policy in case I was nervous about my water source.

I bought a Steripen a couple years ago, just as an insurance policy to take on a trip where I did not know if I might find myself away from a designated drinking water source. Never needed it, but I was glad to have it along anyway. It meant that I did not feel it necessary to carry a lot more water all the time as a contingency. And since I did not plan to use water from a stream or lake, I did not want to bring the larger or heavier filter, I was only looking for a contingency in very rare situations.

The chlorine bleach or Steripen option (or boiling), those are only good for biological contaminants, not chemical contamination. Thus, if your concern is industrial pollutants, in that situation you would need something else.