The water that goes into soda taps/machines almost certainly has a filter on it, so it's clear when it comes out and goes into glasses. Guaranteed they are not serving brown water to customers. If they are, then customers are definitely going to complain.

If anything, their filters are going to start to get clogged much faster and they're going to be moving through them more quickly. The mix from carbonated water to syrup will be thrown off and everything will taste sweeter or "more chemically" for diet sodas and customers will also complain.

ETA: Source is that I've watched distributors and inspectors test and inspect soda machines, test the water to syrup ratio, and we would get dinged if the soda mix was off, which may have been because of clogged filters that weren't performing as expected (water flowed slower and the syrup mix was left as-is). If we received more than a handful of points, the distributor or brand (Coca-Cola at the time) would fine us and threaten pulling their products. It was usually fixed by simply replacing the filter, restoring the water pressure and returning the water-to-syrup ratio back to the intended mix.