Most developed countries tap water are fit to drink. Yes, the water will contain chemicals that have been added to purify etc, but they are fit to drink. As I mentioned in the article, it is a matter of choice in taste. In the USA, some States have their water smell of chlorine, but that does not say it is not drinkable. And in some areas in the UK, tap water is hard water, even then it is safe to drink.
There’s no reason to choose bottled water over tap water or to further filter and purify tap water in developed countries. People just do this, and I will say it is a waste of money.
Dasani and Aquafina, use local municipal water by further filtration known as reverse osmosis. They were banned in the UK, as it is not ethical to sell tap water as bottled water, but it is well accepted in the USA.
And your second question, yes, water treatment and supply in a country is a rather elaborate and expensive issue. The country must make it a priority. In most developing countries, the government is corrupt and always get their priorities wrong, but it can be done if they make it a priority. Bill and Melinda Gates Foundation is giving grants to get this done across developing countries.