Salary
Average Salary: $55,000
Expected Lifetime Earnings: $2,296,140
College water polo coaches typically earn about $55,000 (source).
High school coaches make about $30,000 a year, $60,000 if they're also full time teachers (source). Remember, if you decide to teach, there's also a nice pension in it for you. It doesn't seem like much now, but you'll be thanking us when you're fifty and your hips are shot from all that eggbeatering.
If you're an Olympic athlete who hosts fabulously successful water polo clinics, you might be able to make a decent living capitalizing off of your extensive experience playing. The thing is, there's literally only a handful of people in the U.S. doing this. One handful.
If you absolutely don't want to coach or teach, maybe you want to look into being a lifeguard, if you need to spend your days submerged.