# What is the white substance left behind after boiling down water

I was boiling down water in a stainless steel pot as an experiment the other day. When the water was completely vaporised, a white substance was left behind on the bottom of the pot. I tried rubbing it off the bottom, but it would not come off. I'm unsure what this substance is. What is this substance?

• Welcome to chemistry.SE! If you had any questions about the policies of our community, you can ‎visit the help center or take a ‎‎tour of the website. Jan 25, 2015 at 18:49
• I had the same problem. Just added enough white vinegar to cover the bottom of pot and let it sit for about 5 min. Then I added some Ajax type kitchen pot cleaner and it all came out. The cleaner alone did not work. The vinegar did the trick. ![enter image description here](i.stack.imgur.com/0JUjX.jpg)
– user35380
Sep 28, 2016 at 1:26

• Or you can use $\ce{HCl}$. Oh no no no, wait. Perchloric it is! :D Jan 25, 2015 at 20:44