Get useful water information
Bring recent laboratory or treatment-provider results, including the hardness measurement and any other results relevant to the manufacturer's water-quality requirements. Note existing treatment equipment and its maintenance history. A private well and a municipal supply should not be assumed to have the same water conditions.
If you do not have usable results, ask a qualified well or water-treatment provider which testing is appropriate for this supply. A water heater is not a substitute for evaluating the water itself. Keep water-treatment recommendations tied to measured findings rather than a sales demonstration alone.
Ask for a model-specific care plan
Have the heater provider identify the tank-care requirements, inspection intervals, and any limits affecting coverage. Ask whether there is evidence of sediment, corrosion, a leak, or another problem, and request photographs or written findings where available.
Filter care and tank care address different parts of the equipment. Do not assume that a clean air filter establishes the tank's condition. Leave draining, hot-water and pressure-related service, and internal component work to a qualified provider unless the exact owner instructions clearly assign a safe task to you.
Compare treatment and replacement separately
If treatment is recommended, ask what measured condition it corrects, who maintains it, and how it fits the heater manufacturer's requirements. Have the heater and treatment providers coordinate that decision.
A replacement may address a failed heater while leaving the same water problem in place. Your next step is to assemble the model, care history, and water results, then request a written maintenance plan and a condition-based recommendation. That gives you a useful decision without an unsupported lifespan promise.