One thing can be said about water -- if there's a way out, water will find it. The very smallest leak can lead to thousands of dollars worth of damage if it's not caught in time. If you're a capable do-it-yourselfer and there's existing plumbing in place, you can probably manage some minor repairs like changing a shower head or replacing a faucet. Even installing a new toilet is within the realm of a capable DIY-er (just make sure you have a tight seal). Where you can get into trouble is if you try to modify your plumbing system -- extending hot water lines or re-routing your sewer pipes. Working with hot water means copper pipes, and that requires a blow torch. Unless you have some serious welding experience, it's best to leave the torch jobs to the professionals. While this isn't as dangerous as electric work, plumbing problems can get out of hand fast and lead to an expensive and wet future.