Go look at the water heater in your house or the one at work. Not just "I know where it is" — actually read the label on it.
Here's what I want you to find:
1. What year was it made? (Serial number tells you)
2. Is it gas or electric?
3. What's the tank size? (40, 50, 75 gallons)
4. When's the last time the T&P valve was tested?
If it's older than 10 years and you've never checked the T&P valve, that's your weekend job. Flip the lever up for 2 seconds and make sure water actually comes out. If nothing comes out, or it keeps dripping after — that's a problem that needs fixing.
Most people ignore their water heater until it floods the basement. The ones who last 15+ years get checked on.
Drop a comment with what year your water heater is. Let's see who has the oldest one.