Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you:
What goes in the gutter? 水. But, the reading isn't exactly right. It's みぞ not みず, but close enough to create a hook.
I found a 10,000 yen bill in a ditch beside a coin operated parking space.