Watch for a change in the pattern
Water that no longer reaches the usual temperature, a shorter supply of hot water, or a new sound can help explain the issue. Note when the change began and whether it affects every fixture.
Look at accessible connections
Visible moisture near the heater deserves attention. A connection problem and a tank problem can require different work, so avoid assuming the cause from a puddle alone.
Prepare for the estimate
Have the heater type, model if accessible, and a short description ready. Ask about repair and replacement options after the existing equipment is assessed.