Wickard's use was not purely personal. He grew more wheat than he used, and he sold that excess on the interstate market (or, from a different viewpoint: he sold wheat up to the allowable limit and gave the rest to his livestock). This directly impacted the interstate commerce of wheat, because growing his own wheat meant there was less demand for wheat from other farmers. Scaled up to an entire nation, this would have rendered the wheat control law toothless. Generally, this law has been upheld consistently in this context, though SCOTUS has struck down cases where a good was tangentially related to Congress but the targeted act/good was not actually a commercial transaction (or the avoidance of a commercial transaction, as in Wickard).
As I recall, the argument in the decision, however, was specifically that self-production for personal consumption affects the market (because you're not buying the product that you're producing).
Following that logic, Congress can regulate breathing, so long as there's a market for air.
That would be an incorrect understanding of the ruling and a misapplication of legal logic.
Wickard is limited to cases where there is a tangible good, produced and sold as part of an interstate market. Subsequent cases have limited the scope of Wickard further than that--Lopez held that the transaction or good regulated must actually be a part of an interstate market or would have a direct and discernable impact on the interstate market for the regulated good or transaction.
In the case of air--there are already markets for air in the context of medical treatment and transportation (i.e., airplanes). But breathing is not a transaction since there is no economic exchange nor is it even a voluntary act. Even if breathing could be treated as a transaction, the breathing of uncontained air is one of the few goods that can be classified as purely local (the only other physical goods I can think of that are purely local are real estate and improvements to real estate because they are immovable). Moreover--as breathing is currently free--Congress would have to establish that a market for breathable uncontained air could exist in a meaningful sense.
However, the ICC has been used to regulate water...Theoretically it could even be extended to regulating the act of drinking water that has or would flow through multiple states, but any such attempt would likely not receive sufficient support in Congress to become law, and any court ruling on this point would likely result in a law overruling the decision.
