Whenever you have three "drops" on the left side of a Kanji, or Japanese symbol, chances are that it has something to do with water or some kind of liquid.
Examples include tears, oil, sake, etc. This week's lesson is about ocean or sea. It seems to originate from the combination of water (three dots on the left) and "every" or "always" (the letter on the right, independently used for this meaning), suggesting that "every" wave hits the seashore or that water "always" returns to the sea. If this Kanji is used independently, it is usually pronounced as UMI (oo-me). When it is used with another Kanji, it is often pronounced as KAI, such as Kai-gan (seashore), Kai-sui (sea water), or Kai-zoku (pirate).