One of our agents, Hayden Schoepf, wrote an article on water pollution in parks right after the Flint, Michigan water system meltdown. It's titled, "Water Contamination Coverage in a Park Ins Policy" and explains the limited coverage for such issues provided in General Liability insurance policies.
We insure a couple thousand park owners and only a handful carry pollution coverage. It would be a nice coverage to have, but even with rates as low as $2,500 to $7,000 per park- depending on the size and location of the park, it's typically deemed to expensive for the coverage. Being an insurance agent, I too have worried that more park owners should carry this coverage. Nevertheless, and maybe surprisingly, pollution coverage claims against park owners are very rare. The most common source of such a claim is a sewer backup into tenant owned home(s). Some state's laws define these as pollution events, and other states' laws don't. Whether they do determines whether the pollution exclusion found in general liability policies applies.