Reverse osmosis (RO) is a highly effective purification method that produces exceptionally clean drinking water. This process uses a semi-permeable membrane to remove up to 99% of total dissolved solids, including contaminants like heavy metals and various chemicals. While the resulting water is pure, the RO process also strips away naturally occurring alkaline minerals. This often leaves the water with a slightly acidic pH, typically ranging from 5.0 to 7.0. This low-mineral state can result in a “flat” taste, leading users to seek ways to restore alkalinity and enhance the water’s profile.
Understanding Why RO Water Lacks Alkalinity
The lack of alkalinity in reverse osmosis water stems from the filtration process. The RO membrane rejects nearly all dissolved solids, including alkaline minerals such as calcium, magnesium, and potassium. In natural water sources, these minerals act as buffers, maintaining a stable, slightly alkaline pH, often between 7.5 and 8.5.
When the RO system removes these mineral buffers, the water’s pH balance becomes unstable. The purified water readily absorbs carbon dioxide (\(\text{CO}_2\)) from the air once it leaves the system or is stored. This absorbed carbon dioxide reacts with the water to form carbonic acid, which lowers the water’s pH. The slightly acidic nature of RO water is a consequence of its high purity and lack of mineral buffering capacity.
Many individuals prefer to re-alkalize RO water because the added minerals improve the taste, offering a smoother mouthfeel compared to demineralized water. Restoring minerals also helps mitigate the mildly corrosive nature of low-pH water, which can interact with plumbing over time.
Automated Filtration Methods for Remineralization
The most convenient way to consistently make RO water alkaline is by integrating a dedicated remineralization cartridge into the existing filtration system. These automated post-filters are installed after the RO membrane, acting as the final stage before the water reaches the faucet. This method ensures a continuous supply of treated water without requiring daily user intervention.
Using Calcite Media
One common approach uses media made from Calcite, a natural form of calcium carbonate. As the acidic RO water flows through the Calcite, the mineral slowly dissolves, releasing calcium back into the water. This dissolution process consumes the carbonic acid, which naturally raises the pH to a neutral or slightly alkaline level.
Using Calcite and Corosex Blends
For water requiring a more substantial pH increase, cartridges often use a blend of Calcite and Corosex (magnesium oxide). Corosex is more reactive than Calcite, providing a faster boost to the pH. A common blend, such as an 80/20 ratio, balances the fast-acting magnesium oxide with the slower-dissolving calcium carbonate to prevent over-alkalization.
These dedicated alkaline post-filters restore minerals like calcium and magnesium, often raising the water’s pH into the desired 8.0 to 9.0 range. The hands-off nature of an automated cartridge makes it the preferred choice for those seeking purified, alkaline water directly from their tap. The cartridges must be replaced periodically, typically every 6 to 12 months, as the media slowly dissolves.
Simple Manual Methods for Adjusting pH
For those who prefer a low-cost or non-permanent solution, several simple manual methods can raise the pH of RO water immediately before drinking. These methods require direct addition to the water, making them flexible for adjusting individual glasses or pitchers.
Using Baking Soda
One accessible method involves adding a small amount of food-grade baking soda, or sodium bicarbonate. Baking soda is a natural, alkaline compound that dissolves quickly in water, significantly raising the pH. A typical starting dosage is approximately one-quarter teaspoon per liter of water. Users should test the resulting pH to find their preferred level and avoid over-alkalization.
Using Concentrated Mineral Drops
Concentrated mineral drops are highly concentrated liquid solutions of alkaline minerals and electrolytes. These drops typically contain a blend of calcium, magnesium, and potassium, offering a customizable and portable way to remineralize water. Following the product’s instructions, only a few drops are usually needed per glass to achieve the desired pH increase.
Other Manual Additions
Adding a pinch of trace mineral salts, such as pink Himalayan salt, also introduces alkaline compounds like calcium and magnesium back into the water. While adding lemon or lime juice is often associated with an overall alkalizing effect on the body once metabolized, citrus itself is acidic and will not reliably raise the water’s pH level in the glass. When using any manual method, use a simple pH test kit to confirm the water is within the desired range.