A free water test is often the first thing a softener company does in your home. It can be useful, but it can also be the start of a sale built on a single number you never get to see. The job is to judge the test itself, then judge the recommendation that comes from it.
Ask for the readings in writing
Before you accept any conclusion, ask for the results on paper or in a file you can keep. A spoken summary such as 'your water is very hard' gives you nothing to check. The sheet should list each reading the technician took, with its unit. For softener decisions the usual readings are hardness, iron, manganese, pH, and total dissolved solids. Hardness is commonly reported in grains per gallon or in milligrams per liter, and the two are not interchangeable, so confirm which one you are reading.
Find out what was tested and where
Ask where the sample came from. A kitchen cold tap, a basement hose bib, and a well pressure tank can give different results. A sample taken after a pretreatment stage tells you about that stage, not about your source water. Ask whether the water ran for a while before the sample was drawn. Ask whether the technician used a test strip, a drop-count kit, or a meter, and what range that method is designed to read. A strip that only reads up to a certain level will not show you how far past that level the water actually is.
Also ask whether the test covered iron and manganese. Those metals can change which equipment you need, so a hardness-only reading leaves that question open.
Check the recommendation against the numbers
If the technician recommends a particular unit size, ask how they arrived at it. A sizing figure should come from your hardness reading, your household's expected daily water use, and the grain capacity of the unit being offered. Ask them to show the arithmetic. If the answer is a size with no calculation behind it, or a size well above what the numbers suggest, put that question at the top of your list. A larger unit costs more to buy and can cost more to run, so the reason for the size matters.
Also ask which reading each piece of recommended equipment addresses. If the test showed only hardness, a recommendation for extra stages needs an explanation tied to a specific reading.
Notice how the visit is run
A useful test is not a pressure tool. Ask whether you can take the readings home and think them over without signing anything at the visit. Ask whether the company will test again if you want a second reading, and whether that reading is also free. A company that will not put the numbers in writing, or that makes the test conditional on signing, has told you something about how the sale will go.
Compare two tests before you trust either
If you have had more than one visit, put the readings side by side. Readings from the same tap on different days can differ somewhat, which is normal. A large gap between two companies should have an explanation. Ask each technician how they sampled and what method they used. If one reading came from a well tank and the other from the kitchen, they are not measuring the same thing.
Then compare the recommendations, not the sales pitch. Two companies can read the same water and recommend different equipment. The useful question is which recommendation follows most directly from the readings, and whether it explains its size, its stages, and its service needs in terms you can check.
What to bring to the next step
Keep the written results, the sizing arithmetic, and a short list of questions you still have. If you want to see how independent ratings weigh these factors, the Rating Methodology page explains the criteria and the scale. Use ratings to build a shortlist of providers, then use the readings to decide which recommendation fits your water.