Perhaps you've heard of alkaline water, but wasn't sure what it was. Alkaline is the opposite of acidic, chemically speaking. Understanding what this means requires an understanding of some basic chemistry, including what a pH level is.
To understand what makes a substance alkaline, you first need to understand the measurement of pH. The measurement of pH measures how many hydrogen ions there are, with pure water as a base. Pure water is given a rating of 7; ratings higher and lower than that represent a lower and higher concentration of hydrogen ions, respectively, by factors of ten. So a pH of 6, for example, has 10 times the amount of hydrogen ions than pure water; something with a pH of 1 has 1,000,000 times more hydrogen ions than pure water. Inversely a substance with a pH of 8 has 1/10th the hydrogen ions as pure water.
An alkaline is any substance with a pH rating lower than 7; that is, any substance with fewer hydrogen ions than pure water. This is opposed to an acid, which is any substance with more hydrogen ions than water. The further the pH is from 7 the more of an acid or alkaline the substance is, depending on which way you're going.
Alkaline water, then, is simply water with a pH lower than 7. The simplest way to make water alkaline is to add a substance with a pH higher than water; baking soda is a good example, with a pH of 9, as is bleach, with a pH of 13.
A variety of products on the market claim to ionize water, so consumers can take advantage of the supposed health benefits of alkaline water. There is no scientific basis for such health benefits, according to Mayo Clinic nutritionist Katherine Zeratsky. Doctor Gabe Mirkin of Maryland adds that because of the way the human digestive system works, all foods that leave the stomach are acidic and all foods that leave your intestine are alkaline; as such, the pH level of the foods you eat and the water you drink impact nothing but the pH level of your urine. Essentially, the stomach is so acidic that drinking alkaline water cannot have any meaningful effect.
If you want to measure the pH in your home drinking water, materials to do so can be found at your local hardware, pet and pool stores. Ask for a pH testing kit and you'll be provided with chemicals that can be used to detect pH levels.