The question shows up on health forums and in doctor's-office conversations: does water with very high TDS do harm? Answering it requires separating two planes that tend to get confused — safety and suitability. Within regulatory limits, high TDS is not dangerous. But it may be unsuitable in specific contexts. The number is neither villain nor virtue; it is information.
The common confusion
High TDS does not mean dirty water. It means water with many dissolved salts — which may all be beneficial. Mineralization is confused with contamination, and they are distinct things: TDS measures minerals and salts, not impurities or micro-organisms. Highly mineralized European sulphate waters are, in some cases, sought precisely for their composition.
What the regulation says
In Brazil, the sanitary standard sets a reference limit of 1,000 mg/L of total dissolved solids for drinking water.
The World Health Organization (WHO) does not set a mandatory health limit for total dissolved solids (TDS) in water. This is because TDS, on its own, is considered an aesthetic parameter — related to taste and acceptance — and not a direct indicator of health risk. In its drinking-water guidelines, however, the WHO establishes a palatability classification based on the taste of the water:
| TDS level (mg/L) | Taste rating (WHO) |
|---|---|
| Less than 300 | Excellent |
| 300 to 600 | Good |
| 600 to 900 | Fair |
| 900 to 1,200 | Poor |
| Above 1,200 | Unacceptable |
In other words: the limit has more to do with taste than with direct risk.
When high TDS does matter
There are situations in which high mineralization calls for attention: a low-sodium diet, because sodium is part of TDS; kidney disease, because of the osmotic load; the first months of life, out of paediatric caution; and certain kidney-stone conditions, depending on the predominant mineral. In all these cases, reading the report — which breaks down each element — is worth more than TDS alone.
Is low TDS better on principle?
Not on principle. Low TDS means purity, not nutritional superiority. What ultra-low mineralization delivers is a neutral palate, free of interference — and that matters at the table, in pairing with dish and wine, more than in everyday hydration. A medium-mineralization water can be suitable, and even desirable, in the right context.
Conclusion
High TDS does not do harm in itself. It matters in specific contexts, which are assessed by the report. For most situations, the water that fits is the one that suits the moment — and that is a decision of suitability, not of fear.