Group A water systems are regulated under chapter 246-290 WAC and serve fifteen or more service connections or twenty-five or more people sixty or more days a year.

Group A Transient Non-Community (TNC) water systems are regulated under chapter 246-290 WAC and serve a population that changes day to day such as campgrounds, hotels, rest areas, restaurants.  They serve:
Twenty-five or more different people each day for sixty or more days within a calendar year;
Twenty-five or more of the same people each day for sixty or more days, but less than one hundred eighty days within a calendar year; or
One thousand or more people for two or more consecutive days within a calendar year.

Group B water systems are regulated under chapter 246-291 WAC and serve fever than fifteen connections and fewer than twenty-five people per day.