It isn't free but it is less expensive. In fact in Scotland the annual water bill averages to £490 compared to £603 in England. This is despite a lower population density (which means more infra required per person comparatively).
So despite the best efforts of critics, they can't really show that Scottish water is any worse in terms of sewage outflows etc - if anything it is marginally better on that metric, and significantly cheaper to run. And the actual water quality is good, although that has a lot to do with incidental geography. Why would I want it privatised?