Fastio
Fastio is sourced from the Nossa Senhora do Fastio spring within the Serra do Gerês, in the municipality of Terras de Bouro, Braga district, in the Minho region of northern Portugal. The source lies within the Peneda-Gerês National Park, Portugal’s only national park and a UNESCO Biosphere Reserve, in a granitic and metamorphic geological zone. The spring and surrounding area have a long association with pilgrimage and local devotion; the name references an invocation of Our Lady of Fastio. Fastio holds natural mineral water status and is formally classified as hyposaline (very low in dissolved salts), a defined category under Portuguese water legislation.
Mineral composition
| mg/L | |
|---|---|
| Calcium | 1 |
| Magnesium | 1 |
| Sodium | 4 |
| Sulfate | 1 |
| Chloride | 4 |
| Bicarbonate | 8 |
Compositions can vary by season and source. Read our methodology.
Mineral character
Fastio is one of the softest waters in the TWD database. The six standard ions are all at or near detection limits: calcium 1.3 mg/L, magnesium 0.6 mg/L, sodium 4.1 mg/L, sulphate 1 mg/L, chloride 4.2 mg/L, and bicarbonate 8 mg/L. Total hardness is 6 mg/L as CaCO₃; alkalinity is 7 mg/L as CaCO₃. The six-ion sum is approximately 19 mg/L; reported TDS is approximately 54 mg/L, with the difference largely accounted for by silica at approximately 54 mg/L. Silica at this proportion — representing more dissolved content than all six standard ions combined — is a distinctive characteristic, shared with Fiji Water and Waiakea among waters in the database. For blending, Fastio functions as a diluent with negligible ion contribution.
Use-case suitability
- CoffeeNot used in any current coffee recipe. Hardness 6 mg/L is below the 9–266 mg/L range of these targets, useful as a diluent.
- TeaNot used in any current tea recipe. Hardness 6 mg/L is below the 37–59 mg/L range of these targets, useful as a diluent.
- BrewingNot used in any current brewing recipe. Hardness 6 mg/L is below the 26–922 mg/L range of these targets, useful as a diluent.
- BakingNot used in any current baking recipe. Hardness 6 mg/L is below the 46–390 mg/L range of these targets, useful as a diluent.
- AquariumNot used in any current aquarium recipe. Hardness 6 mg/L is below the 35–212 mg/L range of these targets, useful as a diluent.
- HorticultureNot used in any current horticulture recipe. Hardness 6 mg/L is below the 12–54 mg/L range of these targets, useful as a diluent.
Where to buy
PT
Auchan PT, Lidl PT, Intermarché PT
€0.12 per litre
Fastio is available in Portugal at Auchan, Lidl, and Intermarché, typically approximately €0.12 per litre (as of March 2026). Availability outside Portugal is very limited. Sold in still format in PET and glass bottles.