This is a picture by George Morland ,circa 1786, of a family taking tea in the Barley Mow Tea Gardens in Islington, then a separate village, now a suburb of London.

If you look at the picture carefully you can see that behind the lady with the large hat( who is holding a baby) waiter,who is depicted pouring boiling water into a tea pot.

When customers wished to take tea inthese pleasure gardens, they didn't necessarily have to sit at designated spots like the canvas covered dining booths or the dining rooms in the main building of the pleasure gadren.

They ordered boiling water, tea things and tea from waiters who patrolled around the gardens.

They would then bring a tea tray/board full of china in one hand and a kettle full of boiling water to the waiting customer, all the while shouting:

Ware kettle! Ware scaldings!

to warn the other customers in the gardens of the possible hazards of their cargo .(see Walter Wroth, The London Pleasure Gardens of the Eighteenth Century( 1896).

I'm sure Health and Safetly officials these days would have something to say about that, bearing in mind that children,on the evidence of this picture were around leaving toy horses on wjheels and hats as traps for the unwary waiter...;-)