Before your Portuguese Water Dog puppy comes home you should purchase a "crate" or, at the very least, a portable gate to fence off a portion of the house for the puppy. You should crate the puppy whenever you can not supervise his activities. Some people will look at a standard dog crate made of metal or plastic and wrongly assume it's cruel to confine a dog to a small space. In fact, getting your puppy accustomed to a crate has many benefits for both of you. First, it gives your dog a sense of enclosed shelter and security, which it would seek in the wild. (Many an adult dog still retreats to the relative peace and safety of his open crate when the house is full of noisy visitors.) Second, it keeps a young dog from getting into unforeseen trouble when you're not around. And third, it is a tremendous aid in housebreaking. It is not, however, an instant housebreaking solution. While it's generally true that a dog will not soil the place where he sleeps, it can take a while for a puppy to catch on to that idea. I would use the same size crate that he will grow up with but divide it so that he only has a place to sleep. If it is left big and roomy then he may use the far side to do his business.
Remember that until he is 12 weeks old most pups can not control himself as their bladders are not fully formed.
From the very start, while dog training consists of both positive and negative (reward the good and reprimand the bad) aspects, it is to everyone's benefit to stress the positive side.
You need to know the signs of when your puppy is about to eliminate - crouching and straining after play or circling after eating and drinking . Then you need to get him outside at the right time by walking him, kenneling him or even quickly carrying him. Remember, the dog cares only about convenience at this point, so getting him to relieve himself to your satisfaction depends on how good you are at being in the right place at the right time. However, when you verbally praise him for a job well done or even give him a tiny treat, you increase is desire to cooperate. Repetition with no mistakes is the key to teaching your dog.
From the dog's perspective, relieving himself in the house is not a "wrong" behavior. So to avoid these frustrating accidents, make sure he is contained when you are unable to observe him.Another possibility is to attach your puppy to a six or eight foot leash and keep him with you as you go about your daily chores. If, despite your best intentions, he makes a mistake (remember, by your standards and not his!), then a firm shake on the nape of the neck coupled with a forceful "No!" and immediate removal outside should work.
Someone recently told me about a friend of theirs who had trained her pup to ring a bell. She tied a bell at the puppies height to the door knob. Then every time she would take him outside she would first hit his paw at the bell and said good boy and took him right out. He soon learned that ringing the bell got his owners attention to let him out.