Once water has been through a membrane or a still, adding minerals back is a small job with three practical methods. They differ in how much control you have over what goes in, how much attention they need, and whether the result is consistent from glass to glass, which matters more for some uses than others.
An inline cartridge
The standard household method: a cartridge of calcium and magnesium bearing media fitted last in the stack, after the membrane and any polishing carbon, that water passes through slowly and dissolves a little of. It needs no attention beyond replacement on schedule, produces a consistent result while the media lasts, and adds a modest amount. Its limitation is that you cannot adjust what it adds, and its failure mode is silent: the media is consumed rather than blocked, so it simply stops working.
Mineral drops
Concentrated solutions added to a jug or a glass by hand. The attraction is control: you decide how much goes in and, with some products, which minerals. That suits aquarium keepers and anyone matching a specific water profile for brewing or coffee. The drawback is that it is a manual step every time, so consistency depends on the person doing it, and it treats only what is in the container rather than everything from the tap. For everyday household water it is more effort than most people sustain.
Blending
At whole house scale, the usual approach is not a cartridge at all but blending a controlled proportion of untreated water back into the treated stream, which restores mineral content and stabilises the water before it enters pipework. It costs nothing in consumables and is adjustable, and it reintroduces whatever the untreated water contains, so it suits situations where the treatment was for hardness or dissolved solids rather than for a specific contaminant that must not return.
Why any of it is done
Two honest reasons. Taste: the USGS describes hardness as dissolved calcium and magnesium, and those are much of what gives water its character, so restoring a little brings back the flavour people expect in water, tea and coffee. And stability: demineralized water is mildly aggressive to the metals it touches, which matters little on a short tubing run and considerably at whole house scale. The health claims attached to raised pH deserve scepticism. Our softener guide covers hardness across a house.
Questions people ask about remineralization water
What is the simplest way to remineralize?
An inline cartridge fitted last in the stack. It needs no attention beyond replacement and gives a consistent result.
When are mineral drops worth it?
Where control matters: aquariums, brewing and coffee, where a specific water profile is being matched.
What is blending?
Returning a controlled proportion of untreated water to the treated stream, which is the usual approach at whole house scale.
Why remineralize at all?
For taste, since minerals give water its character, and for stability, since demineralized water is aggressive to metals.