「水」 (mizu) means "water." It's a clear, colorless, odorless, and tasteless liquid essential for all known forms of life. You use 「水」 when asking for a glass of water or talking about drinking water. 「水をください。」 (Please give me water.) is a common request.

透明(とうめい)で、生き(い)るために必要(ひつよう)な液体(えきたい)です。飲む(の)時(とき)や洗う(あら)時(とき)に使(つか)います。