What is Alkaline Water? - Definition, Benefits & Side Effects

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  • 0:02 Acid-Base Chemistry
  • 1:57 Alkaline Water
  • 3:32 Benefits & Side Effects
  • 5:09 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda has taught high school Biology & Physics for 8 years. She received her M.Ed. from Simmon's College and M.S. from Tufts in Cellular and Molecular Physiology.

This lesson is on alkaline water, a controversial topic in health and science communities. Here, we'll learn what alkaline means, talk about alkaline water, and explore the debate on alkaline water.

Acid-Base Chemistry

Walk into a convenience store and go to the drink cooler. You'll probably see an array of choices for water. I know my local store has about ten different kinds. What's up with all these waters? Natural spring water is much higher priced than the generic brands, but it also boasts to be from natural springs. Water from natural springs is called alkaline water.

To understand the recent trend of alkaline water, we need to understand some fundamental acid-base chemistry. Alkaline water has a higher pH than other sources of water, so let's start with what pH means. pH measures the concentration of free hydrogen ions in a solution. The equations for analyzing the concentration of hydrogen ions are complex, so the number we use for pH is inverse to (or the reverse of) the amount of hydrogen ions in the substance. Having a lot of hydrogen ions means the solution is very acidic and that it has a low pH. Solutions with very few hydrogen ions are not acidic and have a high pH.

We call solutions that have a low pH acidic, and we call solutions that have a high pH basic, or alkaline. Basic solutions have a lot of hydroxide ions, which have a negative charge. The scale for pH ranges from 0 (the most acidic) to 14 (the most basic). A solution with a pH of 0 is pure sulfuric acid, or close to the acid in our stomachs, which has a pH of 1.5-3.5! A solution with a pH of 14 is pure sodium hydroxide. Our bodies, for reference, have a pH around 7, and most tap water is a similar pH. Alkaline water, in contrast, usually has a pH around 9.

Alkaline Water

Alkaline water is water that is slightly basic. It contains basic minerals such as calcium, magnesium, or bicarbonate. These compounds bind to hydrogen ions in solution, making the water more basic.

So, how do we get alkaline water if normal tap water is at about neutral pH? Natural alkaline water sources are usually springs, or a reservoir of natural water underneath the earth's surface. The rock structures holding the water may have basic minerals, such as calcium or limestone, that leak into the water, increasing the pH. Some companies, such as Poland Springs, have their own springs that they bottle water from. The Mammoth Hot Springs in Yellowstone National Park are examples of alkaline springs.

Some companies add minerals to the water to make it more basic. Water can also be ionized, meaning it is broken up into hydrogen ions and hydroxide ions. The hydrogen ions are bound by minerals in the water, which makes the water more basic.

However, not all ionized water has these minerals. Tap water that has been ionized will not have a lower pH, because there are no minerals to attach to the hydrogen ions. Similarly, people can buy machines that ionize tap water at home, but without the minerals present in the water, there will be no change in pH. Some people try to add baking soda to water at home, which is also a base. This is not the same as alkaline water, because there are no minerals present, and this method is not recommended.

Benefits & Side Effects

Alkaline water is controversial, but some people believe it has many health benefits. This belief is in spite of the fact that there is little scientific evidence to back this up. The benefits people claim include decreased risks for diseases, like cancer; preventing aging; and boosting metabolism. However, none of these claims have been verified in scientific studies.

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