You aren't being forced at gunpoint by the IRS to drink tap water. You are free to buy whatever water you want. You are being forced to buy insurance. A very big difference.
Under the new health insurance law, the penalty for not buying health insurance is a fine. I forget the yearly amount: $500-1000 (depending)? Yes, that's a form of force. The amount of the fine and who it impacts is the amount of force. It's economic taxation. It also further opens up a slippery slope in the ability for such forms of force to be used increasingly in other aspects of government and society. That's another topic.
Both propositions are easily argued as forms of force. They could easily be argued as unjustified compared to other systems and methods. However, for now, I'd argue that contaminating water is a larger form of force.