Destroy that Urban Myth

I beg to differ, Stjohn - I've actually seen damage on plant leaves from just this cause - though you're right, it doesn't happen often, the conditions have to be exactly right.

and as water will evaporate from a cold pavement rain drying up in the winter] it doesnt have to be hot. and some plant cells are damaged from about 30 degress centigrade.

so i am more inclined to accept water damage on leaves of those soft leafed plants.

Actually I'm afraid I've managed to do it to a couple of plants. I suspect it depends where you are - the temps in my courtyard, against the pale butter yellow wall, are ferocious.

It happens all the time here in Surrey, we are on a very low rainfall and as you can see by the weather forecast, high temperatures. It is not only soft leaves which get scorch, street trees lose many leaves. I have seen the whole side of a Cedar scortched when irrigation has been put on at mid-day. In my younger days, one of my biggest mistakes was watering lettuce overhead in hot sun.

Street tree leaf scorch is due to lack of water due to paveing stones and tarmac stopping enough water penetrating to the roots. This stresses the trees which shows up as leaf scorch, leaf loss and twig or branch die back.
Conifer leaf scorch is also due to lack of water. With not enough water in the tree and leaves, spraying with water increases evapotransporation (water loss through leaves by evaporation), therefore dessicating the leaf which will not show for a few weeks. This leaf scorch is not due to magnification of sunlight through the leaf and burning the leaf.
Potted plants leaf scorch is also due to the plant not receiving sufficient water through the compost causing the water droplet to heat up and can induce a reverse osmosis drawing more water out of the leaf as the drop evaporates causing localised burning. This leaf scorch is also not due to magnification of sunlight through the leaf and burning the leaf.
Conclusion:
Give the plants enough water through the roots and leaf scorch won't happen.
Leaf scorch is not due to magnification of sunlight through the leaf and burning the leaf.
It is due to the plant not receiving sufficient water through the compost causing the water droplet to heat up and inducing a reverse osmosis drawing more water out of the leaf as the drop evaporates causing localised burning.
Destroy the myth.