Lauren Bowker has produced an instructional video with The Lost Explorer in which she demonstrates the step-by-step use of red cabbage dye as a pH indicator. She shows at the end of the video how t-shirts washed in water from different locations will be a completely different color based on the water pH. Lauren’s work has been featured a number of times on Adafruit, but this is a little different than her high art as it is super DIY friendly.

Via The Lost Explorer :

HOW DOES THE CABBAGE DYE WORK AND WHAT DOES IT MEAN?

LB: Red cabbage juice contains anthocyanin and can be used as a pH indicator. It’s red, pink, or magenta in acids, purple in neutral solutions, and ranges from blue to green to yellow in alkaline solutions. Anthropogenic causes of pH fluctuations in our water are usually related to pollution in the air, soil or directly into the water. Acid rain is one of the best-known examples of human influence on the pH of water and it comes from the reaction of water with nitrogen oxides, sulphur oxides and other acidic compounds, lowering its already slightly acidic pH. These emissions usually come from mining and smelting operations or fossil fuel combustion. Wastewater discharge that contains detergents and soap-based products can also cause a water source to become too basic. So the t-shirts, by changing colour, are a really good way of figuring out the state of the local water.