I wash my barrel with water and have no problems. As for the bolt, I have the orginal stock bolt (made of Delrin) and the DEZign bolt (made of Ertalyte), and for both I just swab with some rubbing alcohol and that's it. Though I'm sure cleaning it in water should be no problem.
I think the thing about water was the concern over water absorption into the bolt and causing it to expand. Somewhat over reactive to say the least.
Delrin is a derivative of Acetal and I quote "Because acetal absorbs minimal amounts of moisture, its physical properties remain constant in a variety of environments. Low moisture absorption gives excellent dimensional stability for close-tolerance machined parts. In high moisture or submerged applications, acetal bearings outperform nylon 4 to 1. Acetal is ideally suited for close tolerance mechanical parts and electrical insulators which require strength and stiffness. It also offers resistance to a wide range of chemicals including many solvents."
Read all you want about it here: http://www.dsmepp.com/products/namer..._namerica.html
In only extreme hot water conditions is there a danger for expansion...we're talking boiling water! If you want to be extra careful wash it in warm water instead of hot. But all in all you should have no problem...Like FreeAgent said, just be sure it's totally dry before putting it back in.