If your water heater isn't working, there are several things to check. First, ensure the power supply is functioning, either by checking the circuit breaker or pilot light for gas heaters. Verify the thermostat settings and make sure they're appropriate. For gas heaters, ensure the gas supply is on. Check for any visible leaks or signs of corrosion. If you're not getting hot water, the heating element (for electric heaters) or burner (for gas heaters) might be faulty. If troubleshooting doesn't resolve the issue, it's best to call a professional plumber for inspection and repair.