Systems guides

Four systems, four different jobs

Water treatment equipment is sold as a category and works as a set of separate tools. A softener exchanges calcium and magnesium for sodium. A carbon filter adsorbs chlorine, taste and some volatile organics. Reverse osmosis pushes water through a membrane that rejects dissolved solids. A sediment filter catches grit before anything else clogs. Buying the wrong one is the most expensive mistake in the category.

System	Removes	Does not remove	Typical size
Ion-exchange softener	Calcium, magnesium (hardness), some iron	Chlorine, nitrate, bacteria, most metals	24,000–64,000 grains
Carbon filter (GAC or block)	Chlorine, taste, odour, some VOCs	Hardness, nitrate, dissolved salts	4–20 inch cartridges
Reverse osmosis	Most dissolved solids, nitrate, lead, sodium	Bacteria (without UV), chlorine (needs pre-filter)	50–100 gallons/day
Sediment filter	Sand, silt, rust particles	Anything dissolved	5–50 micron

How a softener actually works

Hard water passes through a bed of resin beads charged with sodium ions. Calcium and magnesium bind to the beads and sodium is released in exchange. When the resin is exhausted, the control head draws brine from the salt tank and flushes the hardness minerals to drain — the regeneration cycle. Capacity is measured in grains: a 32,000-grain unit removes 32,000 grains of hardness before it must regenerate.

Sizing is arithmetic, not guesswork. Multiply household hardness in grains per gallon by daily gallons, then multiply by days between regenerations. A family using 240 gallons a day at 12 grains needs 2,880 grains a day, or about 20,000 grains for a weekly cycle. A 32,000-grain unit leaves margin; a 24,000-grain unit runs close to the limit and regenerates more often.

Where each system sits in the house

• Sediment filter first, at the incoming line, to protect everything downstream.
• Carbon filter next if chlorine is present — chlorine degrades softener resin and RO membranes.
• Softener after carbon, before the water heater, so scale never forms in the tank.
• Reverse osmosis at the kitchen tap, fed by softened water, with its own storage tank.
• UV steriliser last, if a lab test shows bacteria; it does nothing for chemistry.

The order matters more than the brand. A softener installed before a carbon filter is protecting the filter instead of the house; an RO unit fed with hard water scales its membrane and loses output within a year.

Well water changes the list

A private well adds three variables a municipal supply does not have: iron and manganese (staining), sulfur (odour), and bacteria (health). Iron needs oxidation before filtration; sulfur needs aeration or a specific media; bacteria need disinfection and a UV unit. A softener alone will not fix any of the three, and a softener installed on water with high iron will foul its resin.

Test first, then specify. The problems hub maps each symptom to the test that proves it, and the cost hub carries the installed price bands for each component. If you are choosing between formats, the comparison hub puts softener, filter and RO side by side.

Do I need a whole-house system or just a drinking-water filter?

Whole-house if the problem is scale, staining or odour in every tap. Under-sink RO if the only concern is what you drink and cook with. Most homes with hard water end up with both.

Can one unit soften and filter?

Some combination units exist, but they are a softener with a carbon pre-filter in one cabinet — not a substitute for a proper sediment stage. Read the removal spec, not the product name.

How long does a softener last?

Ten to fifteen years for the tank and valve, with resin replaced every 8–12 years. Control heads are the usual failure point, and a replacement head costs $200–$500.