Portuguese Water Dogs are from the working Dog class meaning they are a highly energetic dog and extremely intelligent. No doubt you have done some research and already know this. One needs to really consider the intelligence of this breed. They are very easily trained, but can outsmart the owner if one becomes lackadaisical. Therefore, obedience training is a must.
My experience has been they make great companions and guardians, learn very quickly (both good or bad behavior), very loving and extremely loyal. Quite often due to their innate retrieving aptitude it is quite normal to find them fetching socks, hats, gloves, shoes and other handy items, but on the more serious side they can get a bit nippy as they are learning what is acceptable. Learning this begins with mother and litter mates.