Unfortunately, that is incorrect. Ever heard of acid rain? Acid rain is rain, snow or fog that is polluted by acid in the atmosphere and damages the environment. When substances such as sulphur dioxide and nitrogen oxide are released into the atmosphere, they can be carried over long distances by prevailing winds before returning to the earth as acidic rain/snow/fog/dust. I live in Ontario, which is a part of the Canadian Precambrian Shield, and we get acid rain. Over half of Canada consists of susceptible hard rock areas that cannot neutralize the effects of acid rain.
We are not the only ones who get acid rain. Sulphur dioxide (SO2) and Nitrogen oxide (NOx) are produced not only by industrial sources (like you said), but also by transportation (cars), electric utilities and fuel combustion. So unless your area has no such contaminations at all (which is impossible, unless you don’t have cars or you don’t use electricity), your rain is not as Fresh as you think. Even If your area doesn’t have cars and doesn’t use electricity, the rain that evaporates into the atmosphere doesn’t just stay in one place. The rain you get today might be the water that was evaporated from elsewhere yesterday. You still stand the chance of getting acid rain.
When the water/liquid on earth is evaporated, it doesn’t imply that the evaporated water is clean and the dirt is left behind, and the rain that comes back down on earth is fresh. If that is the case, I can’t imagine why we spend gazillions of dollars on water management. Why don’t we just drink from the ponds in the park or the lakes? It’s Fresh, right? Even after the water management systems, we still spend money purchasing water filters for our taps, because we feel that the water is still not clean enough to drink. That’s not my idea of fresh.
Yeah it’s true that wild pigs do feed on grass and other wild plants that are watered by the rain. Before humans invented houses, we used to live in the wilds inside caves and such. But why don’t we do that anymore? Why do we need to buy houses to live in and stoves to cook our food? Because that’s called evolution. We do what we do now because we feel more comfortable this way. I bet the pigs would enjoy living under our care than in the wilds (except for the freedom). And under our care, we can make the choice of giving them what they used to have, or giving them the best that they could have. I choose to give them the best that they could have.
I’m just saying, *I* prefer not feeding my pigs any grass from my contaminated lawn, and *I* prefer giving them fresh vegetables from other sources. You never know what’s been onto your lawn. Squirrels with mites and lice and whatnot, birds that just took a swim in the sewage, you get the idea. But if you think that is good enough for your pigs, and you think that the grass in your lawn would do, so be it. The ultimate choice is yours.