A water treatment installer will connect equipment to your plumbing, and often to your drain and electrical lines too. Before you sign, confirm that the person doing the work is licensed where your home is, insured for damage a bad installation could cause, and working under a permit if your local office requires one. These checks take a few phone calls, and they are much harder to sort out after the walls are closed.

Ask for the license number, then check it yourself

Ask for the installer's license number and the name it was issued under. Look it up on the issuing agency's own website, or call the agency, rather than relying on a copy someone sends you. Check that the name on the license matches the company on your written quote and the company that will send the crew. If the job involves plumbing or electrical work that the installer subcontracts, ask which licensed business will do each part. A license for one trade does not cover the other.

Ask for proof of insurance, not a verbal yes

Ask for a certificate of insurance that lists general liability coverage and, if the company has employees, workers' compensation coverage. Ask the insurer to send the certificate directly to you, or call the insurer to confirm the policy is active and covers the dates of the job. Ask whether the policy covers water damage caused by the installer's own work. An expired certificate, or one that names a different company, is a reason to stop and fix the problem before any money changes hands.

Find out whether a permit is required

Many local jurisdictions require a permit for changes to water supply, drain, or electrical connections, but the rules vary, so check them for your address. Call the building or plumbing office that covers your property and ask two questions: does this type of work need a permit, and who is responsible for applying for it. If the installer says no permit is needed, ask them to confirm that with the office in writing, or ask the office directly. If a permit is required, ask who schedules the inspection, what the inspector checks, and what happens if the inspector asks for a change after the work is done.

Compare the answers across bidders

Installers who are set up correctly tend to answer these questions quickly and plainly. Vague answers, reluctance to provide documents, or pressure to start before the paperwork is checked are reasons to slow down. For each bidder, write down the license number, the insurer's name, the policy dates, and the permit status, then place those notes next to the quotes. A lower bid that cannot show these items is not a true comparison with a bid that can.

Before the first day of work

After you choose an installer, confirm that the license and insurance match the company actually sending crews, and ask that any permit number be written into the job paperwork. Keep copies of the license, the insurance certificate, and the permit with your equipment records. If an inspection is scheduled, plan to be home, or have someone there who can answer questions about where the new lines run and how the equipment is connected.