Yes, a WaterPik of the type you describe is called an oral or dental irrigator. I also use an oral irrigator once a day to clean between my teeth. Oral irrigators are now recommended by many dental professionals because they have been shown to remove plaque and debris very effectively.
Regular irrigation of your teeth and gums will always help you minimise your bad breath, simply because it will help you keep your mouth very clean. In addition, if your halitosis stems mainly from periodontal disease, an oral irrigator will help your gums heal until, eventually – as long as you are having appropriate professional dental treatment parallel to this – you will have your gum disease under control.
However, if you have been using an oral irrigator for a while, you have had (or are having) treatment for gum disease (if applicable) and bad breath is still present, I think this is a sign that your bad breath is probably caused by something else. I replied to one of your other posts, stressing how important is to determine the most likely causes of your problem so you can use the best remedies and treatments to target them. If you can rule out periodontal disease completely, then you can investigate other possible causes, such as the tonsils, sinuses, dry mouth or dental infections, to name a few.
Dolors