Treatment systems

Listed in the order they are installed, because the order is not a preference — each stage protects the one after it.

The short answer

A well water treatment train is a sequence, not a shopping list. Sediment filtration comes first to protect everything downstream. pH is corrected before iron removal, because oxidation barely works in acidic water. Iron comes out before the softener, because it fouls resin. UV goes last, because particles shield bacteria from the lamp.

The stages, in order

Each stage protects or enables the one below it. The three marked junctions are where installing out of order stops the equipment working at all.

1Sediment filtersFirst in the train. Cheap, and it keeps everything downstream alive.First, where the supply line enters the house.2Acid neutralisersStops acidic water dissolving your pipes — and has to go in early.Early — after sediment filtration, before any iron filter or softener.3Iron, manganese and sulfur filtersOxidises iron, manganese and sulfur — and must sit ahead of the softener.After any acid neutraliser, before the softener.4Water softenersHardness only — and it is not a filter or a purifier.After iron removal, before carbon and UV.5Carbon filtersTaste, odour and chemicals — and it saturates silently.After the softener; before UV if both are fitted.6UV disinfectionKills bacteria without chemicals — and fails silently in cloudy water.Last of the whole-house stages, after all filtration.7Reverse osmosisPoint-of-use. The only common stage that removes nitrate and arsenic.Point of use, at one tap. Last of everything.

How many stages does a normal well need?

Two or three. That is worth stating plainly, because a list of seven stages reads like a shopping list and it is not one — it is a sequence, and you only install the parts of it your water calls for.

A well with hard water and nothing else needs a sediment filter and a softener. Add iron above about 3 mg/L and it becomes three stages. A well that has tested positive for bacteria needs sediment filtration and UV, and possibly nothing else at all. The seven-stage system exists, but it is uncommon and it should be justified line by line against a water test.

If a quote includes a stage, it should be possible to point at the number on your test that stage is there to fix. Any stage that cannot be traced to a result is worth asking about.

The four ordering mistakes that cost the most

Each of these is a case of correctly chosen equipment failing because of where it was installed, rather than what it was.

A softener bought for a sulfur smell. Ion exchange has no mechanism for removing a dissolved gas. The smell survives and the money is gone.
An iron filter in acidic water. Oxidation barely proceeds below pH 7, so the filter underperforms from commissioning, gets blamed, and is often replaced by a larger one with exactly the same problem.
UV without adequate sediment filtration. The most dangerous, because it fails silently — the lamp is lit, the system reports normal, and shielded organisms pass straight through.
A softener sized before an acid neutraliser goes in. Calcite raises hardness as it works, so the sizing is done against a number that is about to change.

What a system costs

Stage by stage, most wells land between $900 and $5,000 installed. A softener alone is $800 to $2,500; adding an iron filter takes it to $2,100 to $5,900. Running costs are modest but real — salt, cartridges, media and an annual UV lamp.

Full cost breakdown by stage

Which of these do you actually need?

Almost nobody needs all of them. The right train is decided entirely by what is in your water, and the fastest way to find out is to enter your test results — you get the stages your water calls for, in installation order, and nothing it does not.

Build a train from your test