I have a couple of RO systems and been using them for about 14 years. They have definitely come down in price with the latest from Lazada about 5000 Baht. I replace the ( first filter, sediment) every 6 months, about 50 baht and the rest when the taste changes , about 2 years. Can also add additional Post carbon filters to the stack very cheaply.
Some facts, pure ( good) water has NO taste. People say RO water tastes funny. Hello, something is wrong with the system, suggest maintenance ( not high in Thai DNA). <removed> testing is NOT about quality but how much ( unknown) dissolved chemicals are in the sample.Here is an excerpt from Google AI..
No, <removed> (Total Dissolved Solids) is not a good measure of overall water quality. While <removed> provides a measure of the total amount of dissolved minerals and salts in water, it doesn't indicate the presence or type of harmful contaminants. A low <removed> reading doesn't necessarily mean the water is safe to drink, and a high <removed> reading could be due to beneficial minerals or harmful pollutants.
A working serviceable, well maintained RO system is probably the most affordable drinking water solution.