Water is one of four elements of the zodiac and the other elements are air, earth and fire.
The three water zodiac signs are Cancer, Scorpio and Pisces. If you were born under one of these zodiac signs, then you are a water sign.
Not only can your sun sign be one of the three water signs, but the rest of the planets in your birth chart can also be an water sign. For example, if your moon sign is in Cancer, Scorpio or Pisces at the time of your birth, then you would have a water moon sign.