Here there be spoilers.

This list is abbreviated from ManiacMansionFan:

1. If your copy has copy protection, enter the wrong code on the security door. (Once the alarm starts, if you don't get the right one very quickly, ka-BOOM!)
2. Turn off the power in the basement. Once again, a few minutes later, and ka-BOOM!
3. Drain the swimming pool with the water valve. Once again, a few minutes later, and ka-BOOM! (Are we sensing a pattern yet?)
4. If you have Bernard, and the steel security door is in place (whether or not your copy is copy-protected), have Bernard read the instructions for the door. He'll try to crack it, and ... Oh, OK, you get the point.
5. Get into the secret lab and wait for Dr. Fred to activate the self-destruct mechanism.
6. Enter the Meteor's room without a radiation suit and let the radiation wave hit you.
7. Blow up Ed's hamster in the microwave. Pick up the hamster guts and give them back to Ed. He will not be happy, and that kid will be dead.
8. Copy the tentacle mating calls record on the cassette tape and play it for the green tentacle.
9. Tape Syd or Razor playing the piano, send it to Mark Eteer, and then show the record contract to the green tentacle.
10. With Wendy, get a publishing contract for the meteor, and show that contract to the green tentacle.
11. You already listed this in the question, but for completeness, drain the pool, have a kid climb in it, then refill the pool while the kid is still there. Buh-bye.
12. Fill the glass jar with radioactive water from the pool. Heat it in the microwave. Open the microwave. Enjoy your last few moments with the fumes.

(I should note that many of these can also be avoided once you've triggered them, by undoing the action -- turning the power back on, refilling the pool, etc. -- before the time limit is up.)

Note: this answer contains mild spoilers, but doesn't explicitly solve any puzzles.

In Maniac Mansion, the dead ends are essentially anything that prevents your characters from completing their scenario(s), and getting past Purple Tentacle into the lab.

Here are the general dead ends, which will fail the game regardless of your choice of characters:

• Getting one kid stuck in the dungeon without the key, with none of the other kids being able get into the mansion

• Killing a kid with an important item or ability (or perhaps an important status, such as having a character on your side), or only having one kid left when you need two to solve a puzzle. Obviously, killing any kid should raise serous concerns about your ability to finish the game

• Killing the man-eating plant while you still need it

• Using the paint remover in the wrong place

• Being wasteful/careless with your dimes

There are also some actions that will prevent you completing one or more character's scenarios:

• Exhausting the patience of the Meteor Police

• Failing to develop the film correctly

• Making the envelope unusable

• Not collecting the package

• Not collecting the stamps

• Putting the wrong item in the envelope

Once you have gotten into the lab, there are no "dead ends" - the game will finish one way or another - but you may not have picked up some items you need to finish with a good ending. These items can be collected at any time before entering the lab though.