Hence the asshole comment. You can
always find a way to smuggle a bomb onto a plane. Limiting case: swallow a condom full of plastic explosives and shit it out in the restroom, the same way drug mules carry cocaine or heroin. There's no real way to stop this short of X-raying every traveler.
The questions the TSA should be asking are:
1.) What is the likelihood that a potential terrorist will use this means of smuggling weapons on board?
2.) How effectively can our screening procedures catch weapons, given that they exist?
3.) How much inconvenience does this cost passengers?
People had little problem with metal detectors and X-rays, because 1.) your clothes and carry on luggage are the natural hiding places for a bomb 2.) the machines will catch most of these instances and 3.) they're not a huge hassle for travelers. But by the time you get down to chucking water bottles because there might be a liquid explosive in them and it might be denser than water and it might be non-polar - really, what are the chances that a terrorist will use that means of smuggling? Compared to, say, overvolting a laptop battery?
For that matter, I think metal detectors may also be obsolete, now that it's fairly easy to make plastic/composite knives and guns.