Can Alkaline Water Change Body pH?

It is claimed that consumption of alkaline water provides several health benefits, but there exists a dearth of evidence to support such claims.¹ For some time, I have wondered whether the amount of base contained in various brands of alkaline water could have any significant impact on the pH of the body. After all, I figured that the amount of acid in (or produced by) the human stomach could easily neutralize the small amount of base contained in alkaline water. I decided to do some chemical investigations to see if my suspicions were correct.

I first searched through the scientific literature to find out how much acid is contained in the human stomach under normal conditions. I also looked to see if I could find out how rapidly the stomach produces acid. It turns out that the contents of the fasting human stomach have an average pH of 1.5^2-3 and contain between 35-75 mL of fluid.^4-5 Using the lower of these volumes, this works out to 1.1 mmol of H⁺ in the fasting human stomach:

In addition, the human stomach can produce up to 30 mmol H⁺ per hour after a meal on average.⁶ This means the stomach can replenish the 1.1 mmol of H⁺ present on fasting in only a little over two minutes:

Armed with this information, I tried adding acid in increments of 1.1 mmol H⁺ (0.366 mL of 3 M HCl) to various brands of water (Video 1).

Video 1: Testing Alkaline Water, Tommy Technetium YouTube Channel, May 4, 2022

Given these experiments, claims that alkaline water can significantly alter the pH of your body seem dubious. It appears that stomach acid has no problem neutralizing the small amount of base present in all these brands of water.

I found it interesting that the Fiji brand water had a lower pH than the Essentia brand water, but that it took more acid to neutralize. This comparison of the basic properties of Fiji vs. Essentia water ends up providing a fantastic and simple demonstration of the difference between the strength and concentration of a base. The ingredients list of these waters indicates that Fiji water contains bicarbonate (HCO₃^-, K_b = 5 x 10^-11), while Essentia water contains both bicarbonate and hydrogen phosphate (HPO₄^2-, K_b = 1.6 x 10^-7). By comparing the K_b values for each ion, we see that HPO₄^2- is a much better base than HCO₃^- (over 3,000 times better!). Because of this, small amounts of HPO₄^2- produce much more hydroxide ion (OH^-) than HCO₃^- when dissolved in water:

HCO₃^-(aq) + H₂O ßà H₂CO₃(aq) + OH^-(aq)

HPO₄^2-(aq) + H₂O ßà H₂PO₄^-(aq) + OH^-(aq)

So even though Fiji contains more basic ions capable of reacting with H⁺, the basic ions in the Fiji water ionize to produce less OH^-. To further test this, I titrated the number of protons required to completely acidify each brand of water, both of which contained 700 mL of liquid. Indeed, Essentia brand water only required 0.57 mmol of H⁺, whereas the Fiji water required 1.8 mmol of H⁺. Interestingly, the number of protons required to acidify the bottle of Fiji water matched quite well with the concentration of HCO₃^- listed on its ingredients label (152 mg L^-1 HCO₃^-):

There is so much to investigate here! Are there any other brands of water than have ingredients lists that can be verified upon simple titrations, such as what I did with Fiji water? Are there any brand of water that contain more base than Fiji water? How many protons does it take to neutralize various brands of alkaline and spring water? How many colors of the rainbow can one produce in various brands of and types of  water upon addition of universal indicator – or other indicators?    

In addition to these ideas, these experiments relate to several other chemical concepts. Titrations, neutralization reactions, pH, solution concentration, kinetics, base dissociation constants, and acid-base equilibria…Who knew there was so much interesting chemistry to explore in drinking water?

Happy Experimenting!

References

1. Fenton, T. R.; Huang, T. Systematic review of the association between dietary acid load, alkaline water, and cancer. BMJ Open, 2016. DOI: 10.1136/bmjopen-2015-010438
2. Sammon, A. M.; Ndebia, E. J.; Umapathy, E.; Iputo, J. E. 24-Hour Measurement of Gastric pH in Rural South Africa. Gastroenterology Research and Practice, 2015. DOI: 10.1155/2015/658106.
3. Hartmann, M.; Ehrlich, A.; Fuder, H.; Lüehmann, S.; Emeklibas, S.; Timmer, W.; Wurst, W.; Lüecker, P. W. Equipotent inhibition of gastric acid secretion by equal doses of oral or intravenous pantoprazole. Aliment. Pharmacol. Ther. 1998; 12, 1027-1032.
4. Mudie, D. M.; Murray, K.; Hoad, C. L.; Pritchard, S. E.; Garnett, M. C.; Amidon, G. L.; Gowland, P. A.; Spiller, R. C.; Amidon, G. E.; Marciani, L. Quantification of Gastrointestinal Liquid Volumes and Distribution Following a 240 mL Dose of Water in the Fasted State. Mol. Pharmaceutics, 2014, 11, 3039-3047.
5. Babaei, A.; Bhargava, V.; Aalam, S.; Scadeng, M.; Mittal, R. K. Effect of proton pump inhibition on the gastric volume: assessed by magnetic resonance imaging.
6. Fordtran J. S.; Walsh J. H.; Gastric acid secretion rate and buffer content of the stomach after eating. Results in normal subjects and in patients with duodenal ulcer. J Clin Invest 1973, 52, 645–57.