If your seeing rust on bottom of metal cans, inside the vanity, there is some moisture in it. This may be caused by a cold air duct perhaps located below the vanity or perhaps blowing along a wall and the air is leaking behind and becoming trapped.
If your vanity is located in a bathroom where there is a lot of shower activity the humidity being built up may be the cause. Condensation is caused when the surface of the metal becomes cooler then the surrounding air causing the humidity within the air to condense on the surface. Find the source of the extra humidity or the source of the air that is dropping the temp to allow these items to cool down, and you will have solved your issue.
Does you run a bathroom fan when taking a shower or bath? Does your bathroom ventilate properly?
Your right on thinking about this Steve, If they do not vent the bathroom, assuming it is in a bathroom, The excessive moisture will condense quite easy on the cooler metal cans located in the vanity area.
I need a clarification about a response. I should of stated 1/2 bath, no shower,and bath door is always open, maybe prop open the vanity door? It is the coldest part of house.
If its the coldest part of the home, then you need to correct this. I am betting that the toilet tank also sweats as well?
It takes two things to cause this to happen, cold and moisture.
If the room is cold, it is allowing condensation to form on the metal surfaces as they are the first to get cold and allow condensation to form.
You need to warm up the room, perhaps close off the vent? or lower the humidity within the room where ever its coming from.
If there is no leak, and your sure that this was not the result of placing a wet wash cloth, or having a drip from cleaning the sink top where water dripped down around the faucet, then you need to empty the entire vanity and not place metal cans under there. As I know of no other reason why or how this would occur. Leaving the vanity open may help with the moisture build up there, but the question still is why do you have this moisture in the first place?
Thank you. You were right about the moisture. The bath is close to kitchen,and didn't realize the amount of moisture that comes from cooking. Kept door closed,and moisture didn't accumulate. Thanks again. M
The brilliant Woodbridge saves the day again.
He's always SOOOOO good!