Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word: You're looking at a natural spring in the ground. Water is bubbling up, but then something changes. It looks a bit clogged... something is poking out. Then, all of a sudden, Mario flies out of the springs, falls in front of you and yells: "izumeeeee (いずみ), Mario!"
We're drinking water from the spring.
There are a lot of geese in that spring.
Wow! You look beautiful! Did you go on a special diet? Or did you find the Fountain of Youth?