Uraninite mineralization is not concentrated like yellow cake U238 is. Most granites contain U, Th and other radioactive elements but not to a level that is harmful to people because it's 'diluted' in the granite. Rarely there's mineralizations that are not safe to be around, they aren't common.

Most mined U deposits today meet a threshold where the concentration of U in the rock is enough for the rock to be viable for profit mining. It's usually expressed as a parts per million of U in the rock. The ppm amount where it is profitable to mine a source can change depending on how scarce the resource becomes. Less of a resource means lower ppm levels of the resource become more viable to mine. This WILL happen to U mineralizations in the future it is NOT a renewable resource.

As for natural aquifers they can contain U and radiation varies from aquifer to aquifer. In fact some aquifers (because they can spend more than thousands of years underground) can mineralize U deposits and can be more radioactive than fresher surface waters (some significantly so). There are some old aquifer U deposits that have been mined before. They are also not a common thing. Actually profitable and concentrated U deposits are quite rare.

Also drinking water gets tested. There's standards.

Most people forget that: U235 = bomb U, U238 = fuel U (more stable), but fuel U238 does get enriched with a little U235 to get reactions to kick-off. Also Plutonium is often a waste by-product that can be put back into fuel U as a stand-in for bomb U, Plutonium (which can be made into a bomb) can be re-cycled in the reactor.