World Water Monitoring Day - What's Your pH?

In honor of World Water Monitoring Day, which occurs on September 18, let's talk about pH:

A pH test lets you know if your water is acidic or basic. The scale runs from 0 (very acidic) to 14 (very basic). Natural waters, according to the EPA, usually have a pH between 6.5 and 8.5. On this scale, 7 is the midpoint and it is considered neutral (neither basic nor acidic). Values at either end of this scale (like battery acid, with a pH of less than one, or lye, with a pH of greater than 12) are very hazardous to people.

Image credit: Environment Canada
(who had nothing to do with this blog post but kindly made this nice chart available for reprint)

pH can be measured in different ways, but test strips are commonly used because they are inexpensive and easy to read. You just dip the strip into the water and the strip will change colors. Then you compare the new strip color to a chart of different shades. The color that matches best is a rough guess of your pH. You can pick up pH test strips at your local pet supply store in the aquarium department.

What do the results mean? Let's say that you measured the pH in a stream in your neighborhood and it was below 6. This acidic water might be causing stress to aquatic life like algae and fish. The acids in water might be reacting with metals (copper, lead) in the sediments, causing these substances to enter the water column. Since natural water wouldn't usually have a pH that low*, you'd have a pretty good idea that the water was polluted. Maybe a chemical plant upstream was dumping their effluent - treated wastewater - into the stream and causing these changes. Reporting your findings to a local environmental monitoring agency could lead to finding and stopping the source of the pollution.

Although pH test strips are usually used to check the water in streams, ponds, or your own drinking water supplies, you can test any fluid or even moist solids, like soil. One day, when I was working in a laboratory at college, I stuck one into a can of soda. I remember that my drink had a pH of 3 and I wondered if I should be sticking something so acidic into my body on a regular basis. For reference, the pH of lemon juice is around 2 or 3. Can you imagine drinking a can of lemon juice?

Now, to be fair, lemon juice and soda aren't as close as they seem on the pH scale. The pH scale is logarithmic. With 7 as neutral, that means that a fluid with a pH of 6 would be a 10 times stronger acid than neutral, one with a pH of 5 would be 100 times stronger than neutral, and so on. This image gives a nice sense of the logarithmic nature of the values.

Note to my friends in Texas or New Mexico: In honor of World Water Monitoring Day, Chazimal National Memorial is providing free water testing kits for classes in your area. Each kit has 50 pH and oxygen tests. From their newsletter: to receive your free test kit, contact Chamizal staff at 915-532-7273 ext 130 or email cham_education (at) nps (dot)gov.


* Keep in mind that some areas have acidic water due to naturally occurring conditions - maybe the bedrock or soils near the stream are naturally acidic. If you want to monitor surface water in your area, it's always good to check with your local water quality monitoring groups. They can tell you what values are considered normal for where you live. Check EPA's Volunteer Monitoring page to find a group in your area.