Hi H.,
I didn't read past TL's answer because I also have tears of laughter running down my face and totally agree with her. What a couple of little devils! While I'm laughing too, I can certainly appreciate your frustration. Neither of my kids went to this extreme of "trouble making", but they certainly engaged in their share of inventive disasters. On the bright side, in my experience it's the really smart kids and the ones with amazing leadership potential who engage in the type of behavior you're seeing.
I second TL's suggestion for an area of safe water play. I would recommend investing in a water table and put it some place like your garage or a basement that can withstand getting the floor soaked. Make it clear that this is the ONLY place that water can be played with in the house. Since water tables are shallow and usually don't have a lot of open surface areas (they one's I've seen are usually a series of narrow troughs), you don't have to worry about drowning potential. Also, institute a hard and fast rule about where and how ANYTHING that can squirt or be used to pour liquid can be used. I found that if I wasn't COMPLETELY specific when my kids were small (and even now that they're 18 and 22), those little lawyers would always figure out some way around my restrictions.
I'd like to highly recommend two books for you: Robert Munsch's "Love You Forever" (be ready for your own waterworks if you haven't read this one before), and "The Berenstain Bears and the Bad Habit." You can read both with your kids, but it's the Berenstain Bears method for addressing problem behavior that I found worked really well when my kids were little. It's basically a method for using positive reinforcement to address negative behavior. In a nutshell, you set down ground rules for specific behavior (e.g., no water play in the bathroom -- the sink is ONLY for washing hands and brushing teeth). Then, take each child to the dollar store and have them pick out something they really want to work towards earning, but don't buy it. Next, give each child 1 - 10 pennies, nickles, dimes, or quarters (depending on how fast you want to them be able to attain their goal), and have them keep them in a pocket. These serve as tangible reminders of the "bad" behavior they're not supposed to engage in. Give them as many as you're willing to give them "chances" to remember not to break the rules. Everytime they break the rule in a single day, they have to give up one coin, and are reminded that it will take them that much longer to reach the goal. At the end of the day, if they have any coins left, they get to keep them. The next day, they start fresh with a new pocketful of coins. This helps to teach them that there is always room for correcting mistakes on a day-to-day basis. As they get better at controlling their playful, though inappropriate, impulses, you can reduce the number of coins (tolerance for mistakes) or lengthen the duration for which they must behave (2, 3, 4 days or more/pocketful of coins). When they've accumulated enough change, head to the store to claim the "prize." (This is a great opportunity to introduce the concept of "sales tax" too, if you want to!) If by this time some modification is still necessary, repeat the process. Hopefully, they won't figure out the trick of behaving just long enough to earn the toy!
Good luck! It sounds like you're in for quite a run for your money over the next 14 or so years! You have good health insurance, right? ;-)