Treating water for human consumption, is in many cases diametrically opposed to what fish need. If there are 1 million water drinkers in a city, and 100serious fish keepers, who do you think gets priority.
If you are a serious fish keeper it is your responsibility to keep your fish safe, not your water department. One dead child from non-potable water, your brother, your daughter, your grandfather, would outweigh all the fish keepers dead fish in 1000 cities.
You cannot walk away during a water change, if there is a problem in a distribution system, to keep people safe, the system will be shocked, that cannot be helped. Monitoring water constantly during every water change, is always needed. If you don't neutralize chlorine, you may have been lucky for 20 years, but all it takes is 1 water main break, and your fish will be dead, if you are not dead on the case.
There are also many things that can go wrong at water plants, they are dangerous places, things blow up, gas escapes, **** happens, I worked in one for 20 years, someones guppies are the least of their worries.
People would call our plant every day saying we killed their fish, and because I was the fish guy, I was sent to their homes, and 99.999% of the time, my tests revealed it was the fish keepers mistake, ignorance, or lack of vigilance.
You may notice the OP is from Laos, and I would imagine they have very special water concerns, I spent over a year in Viet Nam, and would get water borne illnesses regularly. For that country to simply get potable water for human consumption, is a giant leap.