Most homeowners start by comparing quotes. A better first question is where the water comes from, because a system that works well on city water can be the wrong tool on a private well, and the provider who quotes it may not know the difference. Before you spend time on totals, find out whether the company has real experience with your source.
Find out your source first
Look at your water bill. If it comes from a municipal utility, you are on public supply. If you pay a well maintenance or pump service, or there is a pressure tank and a pump in the basement, crawlspace, or a utility shed, you are on a private well. Some homes have a city connection with a legacy well still plumbed in, so confirm which one feeds the kitchen tap. Write down the answer and bring it to every provider conversation.
What to ask a provider about your source
Ask direct, specific questions and listen for whether the answers are about your situation or a generic script.
For a city supply, ask how they handle the disinfectant the utility uses. Ask whether they have worked with systems that face free chlorine and with systems that face chloramine, since the two behave differently in carbon media and can change how often media needs replacing. Ask what they do when the utility changes its treatment, and whether they will request the annual water quality report before they size anything.
For a private well, ask whether they will require a current lab test before they quote. Ask which contaminants they test for and whether they have a plan for results that show bacteria, nitrate, or other problems that a treatment system is not designed to fix on its own. A provider who skips this step and sizes from a guess is telling you something about how the rest of the job will go.
For either source, ask what they will do if the test results do not match the design assumptions. The answer should be a plan, not a reassurance.
Check who handles the well equipment
On a private well, the pump, pressure tank, and well casing are often outside the treatment system's scope, but problems there can look like water treatment problems. Ask who diagnoses low pressure or air in the lines, and whether the provider will work with a well contractor or will send you back to one. Get the answer in writing so there is no argument later about whether a sediment problem or a pump fault is the treatment company's job.
How to compare the answers
Put the answers side by side. A provider who asks for your source, requires a test, names the contaminants they will check, and explains what they would do with unexpected results has done the groundwork. A provider who offers a quote before asking any of these questions has priced a product, not your water. If you want to see how we weigh these factors when matching systems to providers, the methodology page explains the approach. To start a side-by-side comparison of providers serving the St. Louis region, go to the Compare Water Treatment home page.