The Toddy System or Cold Water Brewing System is
reasonably common in America 
but, as yet, not well known in Britain.
This system of brewing cold coffee was pioneered in 1964 by Todd
Simpson, a chemical engineering graduate of Cornell
University.
The standard Toddy System consists of a unit with a brewing (or
steeping) chamber and a plug and filter at the bottom, sitting on
top of a glass jug. 1 lb of medium ground coffee together with 3 ¾
pints of cold water are added to the brewing chamber and allowed to
steep for twelve hours. The plug is then removed and the resulting
concentrate is allowed to drain through the filter into the glass
jug below. The resultant coffee concentrate must be
refrigerated.
To make a cup of hot coffee, simply mix one part concentrate with
three parts of hot water or milk (or mix and heat in a microwave
oven). Alternatively it can be mixed with iced water. The
concentrate is good for about three weeks in the refrigerator, and
can be frozen for several months.
Cold brewed coffee is naturally sweet and less acidic than hot
brewed coffee, as certain bitter tastes and aromas in the ground
coffee are not released at such low temperatures. It is also low in
caffeine and very smooth, which makes it more suitable to be drunk
cold. Toddy Products claim some 6,000 coffeehouses throughout the
U.S., Canada and Australia use their proprietary Toddy Cold Brew
System, and, with 67% less acid than coffee made by conventional
hot brew methods, it's much easier on sensitive stomachs.