Question: what is the difference between the composition of tap water and deionized water?
Answer: A: Deionized Water (We call it "DI water" in the chemistry labs) is just what it sounds like: Water that has the ions removed. Tap water is usually full of ions from the soil (Na+, Ca2+), from the pipes (Fe2+, Cu2+), and other sources. Water is usually deionized by using an ion exchange process.