Far from it, actually. Drowning is one of the most unpleasant ways possible to attempt suicide. First you'll try to hold your breath, but you will invariably open your mouth at some point and inhale a lot of water, which will immediately fill your lungs, causing excruciating pain. And you will continue to make it worse as your body naturally struggles for air, causing you to panic and hyperventilate while in water, flooding your entire system. It will take you many minutes to lose consciousness, and every second is an unrestrained and unspeakable agony.
Definitely not recommended. Very far from peaceful.
Would you be willing to tell us what's going on that's causing these thoughts?