What's causing it? The free market is working great to build the systems to get drugs to people. In fact if a pharmacist refused to give out antibiotics when they weren't needed, the pharmacist would probably just go out of business because the customer would just head up the street to the next guy.
The free market is not so hot at building expensive infrastructure like safe water in a tropical biome, that requires government involvement (not meaning to rag on SE Asian governments: building this stuff is difficult even if your country has been stable for the last 100 years, which is a luxury they haven't been lucky enough to have)
It’s not rocket science. You need to:
1. Build, operate, and maintain wastewater treatment plants
2. Require everyone send their wastewater to a treatment plant
Vietnam has a neat loophole for 2. where if you simply generate too much wastewater for your zone’s plant to handle, you don’t have to send it to the plant. That’s more a policy decision with a side of administrative corruption that’s unrelated to who’s handling the infra.
You'd be surprised at how difficult this is in shitty countries.
First, wastewater plants are rather expensive. Maintaining them is also both expensive and required. And you don't get bonus points for doing the right thing.
My home city of Chişinău, Moldova has a population of about 800 000. The whole city stank of feces for almost two years (and districts close to the sewage treatment facility for much longer than that) because no one cared to maintain the old Soviet-built facility.
Only when you could smell (and almost taste) shit over 20km away, did they scramble to do something (ask for more money from IMF/EU, steal most of it, ask for more money, implement a patchwork solution that barely holds)
In a free market, even the river or the sea has an owner (might be a group of people), so you cannot throw your waste on a river that is not yours. But currently rivers are "common" or public property, so the state cannot limit who polutes the rivers unless they provide an alternative. In rich countries, such alternatives exist. In poor countries they just dump waste in public/common rivers.
In poor countries rivers used to be maintained by the community because of a shared interest in them. This works fine in a gift economy. But in a transactional free market economy the communal river is an externality because it isn't privately owned, which requires outside intervention to create a financial incentive (either via subsidies or regulations/fines).
The tragedy of the commons is not a natural law, it's an emergent property of the economical system. There are three remedies: privatization of the commons (which has its limits unless you literally want to commodify every atom in the biosphere), state intervention (which is how most functional mixed market systems approach it) or changing the system (which goes against the interests of those currently benefiting from it and may as well lead to a worse system than a better one).
EDIT: For sake of clarity: creating a gift economy alongside a transactional free market economy is extremely difficult in an open system. They keep being reinvented in peer groups (e.g. buying "rounds" of drinks among friends without keeping tabs on who spent how much) but they rapidly break down when exposed to a transactional system because "freeloading" becomes an optimal move without the "honor system" enforced by social pressure (e.g. your peers thinking you're taking advantage of them and no longer inviting you to drink with them or having a stern word with you).
Antibiotic pills are cheap and easy to distribute.
Probably the main one is the cost of RO but if that cost can be got down it might work.
There are a number of reasons, but one that hasn't been mentioned so far is the heavy use of antibiotics in food production: https://ourworldindata.org/grapher/antibiotic-usage-in-lives...
For my understanding, if no one else's: are there a lot of places without decent water, but with antibiotics? What's causing that strange inconsistency?