Re: Can a drop of water under any curcumstances including sun light cause fire?

Did you know that Eskimoes use a piece of ice to make fire?
They hold the piece of ice in cuped hands till it melts into roughly lense 
shape and use that to concentrate sunlight on lightly flammable material.

To answer your initial question, yes in theory light collected and focused 
through a drop of water could cause fire.
But in practice a drop doesn't stay around long enough to do so.
The surface tension of water (which makes a drop stay in drop from...let's 
say dangling from a faucet) will increase in volume and once the weight is 
larger than the surface tension able to maintain the the shape,so the drop 
falls...And this process doesn't take very long.

But if you wash your brand new car and leave the drops on your paint..the 
sunlight can damage the paint, focused in a water droplet.

Back to your question : Yes a water drop could cause fire ,but in 
practical terms the chance of it is very very slim.