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The short answer
How to remineralize water from an RO system or a distiller: the simplest permanent fix is a remineralization cartridge after the RO membrane, which dissolves a little calcium, and sometimes magnesium, into the water. For a jug at a time, use calcium and magnesium mineral drops. A pinch of salt or baking soda improves taste but adds only sodium. For most people, it’s a taste choice: the WHO says water typically supplies just 5 to 20% of calcium and magnesium intake, and Germany’s risk assessment agency found very low-mineral water has no long-term adverse effects with a balanced diet.
Why does RO or distilled water taste flat?
Both processes remove nearly everything dissolved, minerals included. NSF/ANSI 58 requires a certified RO system to cut total dissolved solids by at least 75% (example data sheet). With no minerals to buffer it, the water absorbs carbon dioxide from the air and turns slightly acidic, much like rain at about pH 5.6. The WHO calls demineralized water highly aggressive, meaning it can corrode metal plumbing, which is why utilities stabilize it.
Do you need to remineralize water for health?
Not usually. The WHO’s current guidelines set no minimum mineral level, citing insufficient data, and say evidence linking magnesium or hardness to heart health does not prove causality. A 2005 WHO-published review proposed minimums (WHO), but Germany’s Federal Institute for Risk Assessment (BfR) called those statements outdated in 2020. Food is the main source: in the US, about 72% of calcium comes from dairy (NIH), and leafy greens, legumes, nuts, and whole grains supply magnesium (NIH). The BfR says three groups should pay attention to mineral intake: people on very unbalanced diets, pregnant or breastfeeding women, and athletes exercising more than 90 minutes.
How do you add minerals back to water?
| Method | How it works | Good to know |
|---|---|---|
| Remineralization cartridge | A post-filter of calcite (calcium carbonate), sometimes with magnesium media, dissolves minerals into RO water. It raises hardness and alkalinity (UF/IFAS). | Replace per the maker; Aquasana says every 6 months for its SmartFlow stage |
| Mineral drops | Concentrated calcium and magnesium added by the drop to a jug or glass. | Flexible; no install; ongoing cost |
| Salt or baking soda | A pinch per liter improves taste. Both add sodium, not calcium or magnesium. | FDA daily sodium limit is under 2,300 mg, about 1 teaspoon of salt (FDA) |
| Blending with tap water | Mix filtered and tap water. | Brings back whatever you filtered out, such as lead or PFAS |
NSF/ANSI 58 certifies what an RO system removes, not what a mineral stage adds back (NSF). No certifier verifies remineralization performance.
How many minerals does remineralizing add?
Not much, in diet terms. Adult magnesium needs are 310 to 420 mg a day, and calcium 1,000 mg for most adults (NIH, NIH). Drinking 2 liters of water at 20 mg/L of magnesium adds 40 mg, about a tenth of a day’s need. Calcium becomes noticeable to taste at 100 to 300 mg/L, far above what a cartridge adds. A TDS meter shows the total rise but can’t tell which minerals you added, since it measures electrical conductivity.
Does remineralizing make water alkaline?
Mildly. Calcite raises pH and buffering as it dissolves (UF/IFAS), moving RO water from slightly acidic toward neutral. That’s not the same as “alkaline water” health claims, which these sources don’t support. The EPA’s recommended range for drinking water is pH 6.5 to 8.5.
Which RO systems add minerals back?
These under-sink RO systems include a remineralizing stage. Check the certification for what each removes; the mineral stage itself isn’t certified.
| # | System | Score | Certified by | Lead | PFAS | Fluoride | Running cost | Price |
|---|---|---|---|---|---|---|---|---|
| 01 | Aquasana SmartFlow ROCertified by WQA, remineralizer stageUnder-sink RO | 4.1 | WQA | Certified | Certified | Certified | $0.49+/gal | See priceon Amazon › |
| 02 | iSpring RCC7AK-BNCertified by NSF International (BN or BLK), alkaline stageUnder-sink RO | 3.9 | NSF International | Certified | Claim | Certified | $90 to $100/yr | $199.99on Amazon › |
| 03 | Home Master TMAFC-ERPTwo-stage minerals, not certified | 2.8 | None | Claim | No | Claim | $419.90on Amazon › |
Certified: Certified by an independent body (named in each pick). Lab test: Tested by a named independent lab, not certified. Claim: The maker's claim, not certified. No: No claim. PFAS means PFOA/PFOS, or Total PFAS where the pick says so.
APEC’s RO-PH90 adds a calcium stage to the RO-90; see our APEC RO-90 review. More options in the best RO systems.
Common questions
How do you remineralize RO water?
Add a remineralization cartridge after the RO membrane, or use calcium and magnesium drops by the jug. NSF/ANSI 58 certifies what the RO removes, not what the cartridge adds.
Do I need to remineralize distilled or RO water?
Not for health if you eat a balanced diet, according to Germany’s BfR (BfR). The WHO says water supplies only 5 to 20% of calcium and magnesium intake.
What is a remineralization filter?
A post-filter cartridge, usually calcite (calcium carbonate) and sometimes magnesium media, that dissolves a small amount of mineral into RO water and raises its pH.
Can I add salt or baking soda to RO water?
A pinch improves taste, but both add sodium, not calcium or magnesium. Skip it on a low-sodium diet (FDA).
Should I remineralize water for baby formula?
Follow the formula label and your pediatrician. The BfR found very low-mineral water used for formula wouldn’t lead to inadequate intake. See the best water for baby formula.
Sources
Prices as of November 1, 2026. Product prices and availability are accurate as of the date/time indicated and are subject to change. As an Amazon Associate we earn from qualifying purchases.