Measurement
Water TDS meter
A conductivity probe reporting total dissolved solids in brewing water. Useful, and routinely asked to answer questions it cannot.
- Type
- Measurement
- What it is for
- Measurement
- Who needs one
- Specialist instrument
- Materials
- Plastic housing, Conductivity electrodes
- Needs attention
- Calibrate at intervals; replace the battery before it drifts.
What it is
A TDS meter measures electrical conductivity and converts it, using an assumed factor, into a parts-per-million figure. That figure tells you roughly how much dissolved material the water carries in total. It does not tell you what that material is, and the distinction matters: two waters reading 120 ppm can behave completely differently in coffee depending on whether the content is mostly hardness or mostly alkalinity.
How it works
Two electrodes measure how readily current passes between them. More dissolved ions means more conductivity. The conversion to ppm assumes a composition.
Why people use one
To check bottled waters against each other, to monitor a filter or reverse-osmosis system's output, and to notice when a supply changes.
What this actually changes
Separated by what it affects, because “improves your coffee” is not something you can act on. Where the evidence is thin or contested, it says so.
Seeing what went wrong
Modest differenceGood at detecting change and at comparing waters. Poor at telling you what to do, because composition matters more than total.
Taste
No differenceIt is an instrument. It changes nothing.
Who it is for
Worth having if
- Anyone running a reverse-osmosis or remineralisation setup who needs to verify the output
- Anyone comparing bottled waters systematically
Probably skip it if
- Anyone who has not yet tested hardness and alkalinity, which are the more informative measurements
- Anyone hoping a single number will diagnose a taste problem
Common mistakes
Treating TDS as hardness
Two waters with the same reading are assumed to behave alike, and they do not.
Instead: Test hardness and alkalinity separately; use TDS to track change.
Cleaning and care
Rinse the probe in distilled water and calibrate against a known standard solution periodically.
What you could use instead
Hardness and alkalinity test kit
Measures the two things that actually determine how water behaves in coffee.
When it goes wrong
Often used alongside
Other equipment this one is used with, or that the same brewing methods call for.
Drinks it appears in
Drinks that name this equipment, or that are brewed by a method requiring it.