[header] How to make your eyes water [title] Cut some onions. [step] Onions soak up sulfur from the soil when growing, and when you chop them up, you break open cells in the onion and release enzymes that mix with the sulfur. This creates an invisible gas that causes a burning sensation in your eyes, causing you to tear up without crying. 
[substeps] Chop some onions and linger over them. Some people are more sensitive than others; you may only need to cut a little bit of the onion, or you may need to really linger.