Here is what actually occurs when alkaline water is ingested: the stomach pH temporarily goes up; however, the stomach has its own happy acid pH level and will try to lower the pH value to its original value by producing hydrochloric acid. This is the homeostasis action. The real question is: how does the stomach produce hydrochloric acid?
The chemical equation for the production of hydrochloric acid by the stomach is: H2O (water) + CO2 (carbon dioxide) + NaCl (table salt) = HCl(hydrochloric acid) + NaHCO3 (sodium bicarbonate).
For each molecule of hydrochloric acid the stomach produces, one sodium bicarbonate molecule (alkaline buffer) is also produced. The hydrochloric acid goes into the stomach and the sodium bicarbonate goes into the bloodstream, thus increasing the alkaline buffer in the blood. The sodium used here is already in the body. We are not adding extra sodium to the body.
As we age, some of us lose the ability to produce hydrochloric acid by the stomach. In that case, alkaline liquid (NaOH) goes into the intestine and is sucked into the blood. This could tend to increase the pH value of the blood. However, when that happens, the acid buffer (H2CO3) reacts with it according to the formula NaOH + H2CO3 = NaHCO3 + H2O. This results in alkaline buffer and water. Could we run out of acid buffer (H2CO3)? The answer is no. H2CO3 is a combination of water (H2O) and carbon dioxide (CO2). As long as we eat carbohydrate, we produce carbon dioxide and this produces carbonic acid (H2CO3) which is acid buffer. We create so much carbonic acid that our lungs must exhale excess carbon dioxide. As long as we live, we inhale oxygen and exhale carbon dioxide.
What is diminishing, as we age, is the alkaline buffer. To maintain the alkaline–acid balance in the blood, we must recharge alkaline buffer in the blood. Drinking alkaline water is the best way. This is better than any alkaline food.