When I first got my PWD he would chew on shoes, dresses and slacks. He would also nip and bite our hands. This was a massive difference with the Black Lab we had for a dozen years. Our lab had the softest mouth, and this new dog didn’t even lick.
We told him “NO!” and maybe even disciplined him, and nothing would help. Were we doomed to years of being attacked?
After a few years, the nipping decreased. Yet even today, when Goji PWD is nearly four years old, he still gets into moods and attacks with his mouth.
I’ve been around many PWD’s and noticed the same thing. I have to state that it is a breed trait, along with jumping. They were trained to grab fishing nets, haul in overboards, grab fish, tug lines, and play hard. It is genetic.
It is very difficult totrain out a genetic trait. It is wrong to scold a dog for something that is natural for him. Scolding will decrease your authority for an instinct. We have to state “Ouch” real loud, not “Bad Dog”. That has helped. When he gets into that attack mood, put on some sturdy gloves. Play with him with the gloves on, he knows they’re gloves and will bite  less when you do not have the gloves on.
Have plenty of chewable, destructible toys around your house for him to attack. The toys are a good outlet for his frustration. It’s a working breed, but few PWD’s  are working. He needs something to do; put a bunch of toys on a dog-bed in his kennel, and let him make a mess of it. It’ssuperior that he makes a mess of his own items than yours. Biting and Nipping is natural for a Portuguese Water Dog.