Many RO purifiers now come with an “alkaline” or “mineral” stage after the membrane. It is also one of the most over-marketed parts of a purifier. Here is an honest look at what it does and what it does not.
Why RO water needs a post-treatment stage
The RO membrane removes most dissolved salts, including minerals like calcium and magnesium. The result is very low-TDS water that some people find flat in taste, and its pH is often slightly on the acidic side. A post-filter adds a small amount of minerals back and can raise the pH a little.
What an alkaline filter actually does
- Adds small amounts of minerals such as calcium and magnesium (and in some cartridges copper or zinc).
- Nudges the pH up – typically towards neutral or slightly alkaline.
- Improves the taste of very low-TDS RO water for many people.
Myths to ignore
- “Alkaline water cures diseases” – there is no reliable evidence for such claims. Treat it as a taste and comfort improvement.
- “More pH is always better” – drinking water standards in India (BIS IS 10500) specify a pH range of 6.5–8.5. Higher is not automatically healthier.
- “It makes the membrane unnecessary” – it does not remove salts, bacteria or chemicals. It only works after proper purification.
How to check if it is working
Use pH test drops or a pH meter on the purified water. If the pH has dropped back to the same level as the water coming straight from the membrane, or the taste has gone flat again, the cartridge is exhausted. Our Water Testing Kit includes a TDS meter and pH drops.
When to replace
Most alkaline and mineral cartridges last 6–12 months, depending on how much water you use. It is convenient to change it together with the carbon filters.
Choosing a cartridge
- Match the length (4 inch, 8 inch, 10/12 inch inline) and the connection type of your old one.
- Copper or zinc-copper cartridges are popular for taste; plain alkaline cartridges focus on pH.
- Place it after the membrane and post-carbon, just before the tap or tank outlet – as your purifier was designed.
See our alkaline and mineral filters (from ₹95).
Frequently asked questions
Is an alkaline filter necessary in RO?
Not strictly, but it makes low-TDS RO water taste better for many people and brings the pH closer to neutral.
What pH should drinking water have?
BIS IS 10500 specifies 6.5 to 8.5 for drinking water.
Can I add an alkaline filter to an old RO?
Yes, an inline alkaline cartridge can usually be added on the outlet line with push-fit joints.
Need help choosing the right part? Send a photo of your RO or its model name on WhatsApp (96252 23245) and we will tell you exactly what fits.
Need the right part for your RO?
Original filters, membranes and pumps at wholesale rates. Send us a photo of your RO – we will tell you exactly what fits.
