And it's not just the gravel/sand that's important. The water itself also differs in its chemical composition (e.g. salts, minerals, basic/acidic pH), which can catch you really dirty when making concrete. Or when dealing with water at all, shout-out to Flint and its infamous water crisis that took eleven years to resolve - every single lead service pipe had to be physically dug up and replaced.

[1] https://en.wikipedia.org/wiki/Flint_water_crisis#2025