I bought a water filter for my tea and it changed nothing

In short

Domestic filters are effective at what they are built for and mostly do not do the thing tea drinkers buy them for. A carbon filter is designed to remove chlorine, taste, odour and some metals; hardness — the dissolved calcium and magnesium that flattens aroma and produces the surface film — is a different problem needing a different mechanism. So a reader whose complaint was chlorine gets a clear improvement, and a reader whose complaint was hard water gets almost none, from the same product.

Likely causes, in order

Most likely first. Answer the question under each one before moving on — several of these look alike in the cup and are told apart only by what was done to the leaf.

1. 1. The complaint was hardness and the filter was a carbon one

   Water chemistry

   Check: Was the original problem a dull flat cup and an iridescent film — rather than a chemical or swimming-pool smell? Does the kettle still scale at the same rate as before?

   Fix: Continuing scale is the giveaway: it means the mineral load is unchanged, so anything that mineral load was doing to the tea is unchanged too. Carbon filtration is the wrong tool for this. An ion-exchange filter or a low-mineral bottled water addresses hardness; the cheapest reliable test is to brew the same tea with a bottled water of stated low mineral content and see whether the complaint disappears.

2. 2. The cartridge is past its life and is passing water through unchanged

   Water chemistry

   Check: How long has the cartridge been in, measured in litres or weeks rather than in intention?

   Fix: An exhausted cartridge does nothing while continuing to look and feel like a working filter, which is the same failure mode as a saturated desiccant. Replace on the stated schedule rather than when the water starts tasting wrong — by then it has been doing nothing for some time.

3. 3. The filter worked and removed the wrong thing, leaving a hollow cup

   Water chemistry

   Check: Is the tea now cleaner but also thinner and emptier — no off-notes, and no body either? Is this a reverse-osmosis or distilled supply rather than a jug filter?

   Fix: Water with essentially nothing dissolved in it makes a flat cup. A moderate mineral content participates in extraction, and stripping it out removes the off-notes and the structure together. This is a real and separate outcome with its own record; the answer is a moderate mineral content rather than the lowest achievable one.

4. 4. The fault was never in the water

   Equipment

   Check: Brew the same tea using a bottled water and a different vessel — a glass rather than the usual pot or kettle. Is the problem still there?

   Fix: If it survives both changes, the water was not the variable and the filter was never going to help. A kettle used for something else, a plastic reservoir on a new appliance, detergent residue and stale leaf all produce complaints that readers attribute to water because water is the easiest thing to change. Each has its own record.

Tea types this applies to

• Green tea

Brewing methods this applies to

• Western brewing (teapot or mug) — A small amount of leaf in a large volume of water, steeped once for a few minutes and then strained off. The approach most English-speaking drinkers already know, and the one most teas sold in the West are made for.
• Mug infuser brewing — Loose leaf in a basket inside a mug — the most common way loose tea is actually made, and the method most often responsible for people concluding that loose leaf is not worth the trouble.

Related problems

Sharing a cause category, a tea type or a brewing method with this one.

• My tea tastes of chlorine, metal or the kettle — A chemical, swimming-pool or metallic note sits over the tea, and it is there whichever tea is brewed.
• My green tea tastes flat and looks dark in this house — A delicate green tea that tasted bright elsewhere comes out dull and heavy here, with a darker, browner liquor than it should have and none of its aroma.
• My tea gets drier and harsher as it cools — The first mouthful is balanced and the last one, several minutes later, grips the tongue and feels rough — from the same cup, with nothing added.
• There are black spots inside my teapot or infuser — Dark speckling inside a spout, under a lid seal, in the mesh of an infuser or around the gasket of a travel bottle.
• My green tea goes yellow or brown in the cup — The liquor is green when poured and turns yellow, olive or brownish within minutes, sometimes with a darker rim.

Sources