It is common practice here in Ireland for 1 Kettle to boil up enough water to provide up to a dozen people with hot tea / coffee at lunchtime.
Firstly, make sure you have enough fuel availabe to boil a couple of kettles and have your cold water nearby.
Boil the kettle as normal which should take approx 5 minutes. Once the kettle has boiled, hold the handle of the kettle at a 90 degree angle to the body of the kettle and lift straight up off the fire base.  Do not lift the handle of the kettle directly above the chimney as this may result in a burn to your fingers.  Once the kettle is clear of the fire base, the handle can be used directly over the chimney and the boiling water carried to your eagerly awaiting customers!  Pour the boiling water into your cups/mugs (3 Pint Kettle approx. 7 mugs / 2.5 Pint Kettle approx 5 mugs / 1.75 Pint approx. 3.5 mugs / 1 Pint approx. 2 mugs).
Refill the kettle with cold water.  If you are camped beside a lake or river, simply immerse the entire kettle into the water to fill the water chamber.  Allow the kettle to drip dry for a brief moment and then, holding the handle at a 90 Degree angle to the body of the kettle, gently lower the kettle back onto the fire base where the fire should still be burning.
Refill the chimney with fuel and hey presto - boiling water again in a few minutes!
This process can be repeated until everyone has drunk their fill.