Every softener choice starts with a few numbers about your water: hardness, iron, and pH at minimum. Those numbers come from your water source, and the source you have decides where to find them. Get them in writing before you talk to a dealer, because the sizing and the scores you read later depend on them.

Find the source first

Your home is usually on one of two supplies, and each one gives you a different starting point.

  • Public utility supply: Ask the utility for its water quality report. Most utilities publish an annual consumer confidence report online, and it lists hardness, often in grains per gallon or in milligrams per liter as calcium carbonate. One grain per gallon equals about 17 milligrams per liter, so check which unit each report uses before you compare anything.
  • Private well: You need a lab test of your own water. Ask the lab for hardness, iron, manganese, pH, and hydrogen sulfide at a minimum. Ask whether the lab reports total iron or dissolved iron, since a softener handles only the dissolved form well.

Check what the number includes

A report can be accurate and still not describe the water you will treat. Ask these questions before you accept a figure:

  • Was the sample taken at the point where your softener would sit, or at a treatment plant or well head that is far upstream?
  • Is the figure an average or a peak? A utility may report a range across the year, and your sizing should use the higher end.
  • Does the report date from before any recent change in your supply? A source switch or a new well pump can change the reading, so ask whether the source changed.

Read the iron and sulfur lines closely

Hardness is the number a softener removes most directly. Iron and sulfur are different. Iron above a low level can coat the resin and foul the unit, and hydrogen sulfide needs its own treatment plan. If either shows up in your results, ask the dealer whether the proposal includes any pretreatment, and get that answer in writing. Do not accept a softener-only proposal for water that carries significant iron without asking how the iron will be handled.

Bring the sheet to the dealer

When you request quotes, send the same test sheet to every company. That way each one sizes the unit against identical inputs, and you can compare the proposals fairly. Ask each dealer which hardness figure they used, which iron figure, and whether they assumed an average or a peak. If two proposals use different inputs, the difference in price or capacity may come from the inputs and not from the equipment.

For a broader look at how ratings are built and weighted, see the rating methodology. For the current company scores in the St. Louis area, see the water softener company ratings.

What to do next

Collect the utility report or the well lab results, write down the hardness and iron figures in one unit, note whether each is an average or a peak, and send that sheet to each dealer you are considering. A good proposal will show how its sizing used those numbers. If a dealer cannot explain the inputs, treat that as a reason to keep looking.