Ozone is an excellent drinking water disinfectant. However, ozone will not render water contaminated by fertilizer runoff or organic chemicals safe. Generally accepted methods (at least at the municipal treatment scale) to remove nitrates/nitrates include methods like ion exchange, reverse osmosis, and electrodialysis. Methods to remove organic compounds like benzene and toluene generally involve a combination of packed tower aeration and activated charcoal. Herbicides/pesticides generally require activated charcoal to remove.

Speaking of the Midwest, Milwaukee converted their antiquated water treatment system to a state-of-the-art system which incorporates the use of ozone after the cryptosporidium outbreak back in 1993. They may have the safest municipal water in the country nowadays.