pH value and alkaline water: what is behind it

What the pH value measures

The pH value describes how acidic or alkaline a liquid is, on a scale from 0 to 14. Pure water has 7, lemon juice about 2, soap about 10. In Germany, tap water typically lies between 7 and 8.5, because dissolved hydrogencarbonate makes it slightly alkaline. The Drinking Water Ordinance (Trinkwasserverordnung) allows 6.5 to 9.5, mainly so that pipes do not corrode. For the body, this range makes no difference.

What the stomach does with it

The stomach works with hydrochloric acid at pH 1.5 to 2. Any drink, whether pH 6 or pH 9.5, is brought to that value there within minutes. The body replenishes the acid as much as it needs. So “alkaline water” does not arrive in the gut as alkaline water at all. An effect is still possible: water with a lot of hydrogencarbonate briefly buffers stomach acid, which is pleasant with heartburn. That is a matter of minerals, not of pH.

Can you “de-acidify” the body?

Blood holds its pH within a very narrow window of 7.35 to 7.45. Lungs and kidneys adjust it every second. Deviations are life-threatening emergencies, not dietary states. What diet can change is the pH of urine, because the kidneys excrete surplus acid or base. That is a sign that the regulation is working, not that the body was “over-acidified”.

What is left of alkaline water

• It does no harm if it comes from a natural spring and is normally mineralised.
• Ionisers that make tap water alkaline with electricity produce water that returns to neutral after minutes, and they cost money.
• Studies on benefits are small, short and mostly paid for by manufacturers.
• If you want to follow an alkaline diet, vegetables, fruit and potatoes do the job far more effectively than water.

When pH does matter after all

For aquariums, plants, beer brewers and coffee lovers. Very soft water with a low pH can attack copper pipes, and very hard water with a high pH scales up faster. If you want to know the value, measure it with a test strip, see Testing water at home. How the other trends stand up is covered in Water trends checked.