Two water test reports can look alike on the first page and still say very different things. One may come from the kitchen tap after a filter, another from the well or the main line, and a third may list only the substances that the company sells equipment to remove. Before you let a report decide which company you call, check the parts that make two results comparable.
Where the sample was taken
Ask where each sample was collected. Water taken before any treatment shows what enters the house. Water taken after a filter or softener shows how that equipment is performing at the moment, and tells you much less about the raw supply. If a company offers only a test of treated water, ask for a test of untreated water as well, or ask them to explain why they do not need one.
Which substances were tested
Compare the list of tested substances line by line. Common ones in home water include hardness, iron, manganese, nitrate, chlorine, pH, and total dissolved solids, though the right list depends on your supply and what you have noticed at the tap. A report that covers only hardness cannot support a claim about iron. If a substance you care about is missing, ask whether the company will test for it or whether it falls outside their work.
Units and reporting limits
Results often appear in different units, and some reports flag readings below a reporting limit instead of giving a number. Hardness might appear in grains per gallon on one report and in milligrams per liter on another. Convert the figures or ask each company to report in the same units. A result listed as below the reporting limit does not mean zero, so check how each report describes those entries before you read them as good news.
Who ran the lab work
Ask for the name of the laboratory and whether it is certified for the specific tests listed. An independent lab report usually carries more weight than a reading taken with a handheld kit during a sales visit, although a kit can still help with a quick check. Ask whether the document is the lab's original report or a summary written by the company. A summary can be accurate, but the original lets you see every line, including anything the summary left out.
Does the recommendation follow the numbers?
Once the reports are comparable, read each company's recommendation against them. A proposal to treat iron should point to an iron result. A proposal for a larger softener should explain the hardness number and the water use it assumes. If one recommendation is much bigger or more complicated than the numbers seem to support, ask why, and ask what the proposal would look like if the test had come back lower.
If you are also using an awards list to narrow your choices, the how winners are chosen page explains how that list was built. Read it alongside the test evidence rather than in place of it.