People generally want a number to compare their reading against, and the honest answer is that there is no health based standard for total dissolved solids, only an aesthetic recommendation concerning taste. That is not an evasion: it follows directly from the fact that the measurement cannot tell you what is dissolved, only how much.
What the ranges roughly mean
Very low readings indicate water with almost nothing dissolved, which is what reverse osmosis, distilled and deionized water produce, and which tastes flat because taste in water comes largely from minerals. Mid range readings are typical of most municipal supplies and of moderately mineralized groundwater. High readings indicate heavily mineralized water, common on hard groundwater, and are usually accompanied by taste and by scale. None of those bands is a safety judgement.
Why a low reading is not proof of anything
This is the misuse worth guarding against. Dissolved solids are measured as a total, so a contaminant present at a concentration that matters for health can be far too small to move the figure at all. Coliform bacteria contribute nothing to a conductivity reading. Nor do most organic compounds. A supply reading beautifully low can carry pathogens or pesticides, and treating a low number as reassurance is exactly the wrong conclusion to draw from it.
Why a high reading is not condemnation
Beneficial minerals count towards the total exactly as much as anything else, so mineral rich spring water reads high and is desirable. Hard groundwater reads high and is a nuisance rather than a hazard. If the reading is high and the water tastes fine, there is usually nothing to act on. The USGS classes water as soft at 0 to 60 mg/L as calcium carbonate through to very hard above 180 mg/L, and hardness is a separate, more useful measurement to take.
Where the number is genuinely useful
Compared against itself. Reading the feed and the permeate of a reverse osmosis system gives a rejection rate that tracks membrane health, and a baseline taken at commissioning makes any later fall meaningful. Tracking one supply over time flags a change worth investigating. Both use the number as a relative indicator rather than an absolute verdict, which is what it is good for. Our TDS level guide covers drinking water specifics.
Questions people ask about water tds levels
Is there a safe TDS level for drinking water?
There is no health based standard, only an aesthetic recommendation about taste, because the figure cannot identify what is dissolved.
Does a low reading mean the water is safe?
No. Bacteria and most organic compounds contribute nothing to the reading, so a low figure is not reassurance.
Is a high reading a problem?
Not necessarily. Beneficial minerals count towards it, so mineral rich spring water reads high while being entirely desirable.
When is the number actually useful?
Compared against itself: feed against permeate on a reverse osmosis system, or one supply tracked over time.