While the city water itself is heavily treated and tested it still has to go through a great deal of pipes before it ends up out of your tap. Especially your house pipes. So there is more variables. Most cities do tests besides just in the storage facility but odds are the majority of the tests are in the pumping stations etc. Before it travels in some cases several miles and then through your own pipes which they have no control over. Especially in older homes that have metallic pipes vs PVC pipes.

Most cities too dont' allow well water to be used and in some ways have a monopoly over who has to buy their services so they don't spend the gazillion dollars on advertising that water companies do. Same reason that a woman that is healthy and in good condition but isn't a size three feels "fat" or why we eat crappy tasting food at "fast food" places that is horrible for us. Unfortunately too often we watch commercials like zombies and follow their commands lol.

Personally the best water I have ever drank was from my mom and dads. Pure artesian fed well over 300 feet deep. Water is so cold it will make feel almost comfortable in the hot Texas sun. Of course they live in the country though so no city water for them.