The black and foully-smelling liquid popularly known as soft water is so rich in carbonaceous and organic constituents as to be of very limited use to the photographer; but by taking the precaution of fitting up a simple automatic shunt for diverting the stream until the roofs have been thoroughly washed, it becomes possible to insure a good supply of clean and serviceable soft water, even in London. Several forms of shunt have been devised, some of these being so complex as to offer every prospect of speedy disorganization; but a simple and efficient apparatus is figured in Engineering by a correspondent who signs himself "Millwright," and as we have thoroughly proved the value of an apparatus which is practically identical, we reproduce the substance of his communication.
A gentleman of Newcastle, a retired banker, having tried various filters to purify the rain-water collected on the roof of his house, at length had the idea to allow no water to run into the cistern until the roof had been well washed. After first putting up a hard-worked valve, the arrangement as sketched below has been hit upon.

License information: nan
MPAA: G
Go to source: http://www.gutenberg.org/files/8559/8559-h/8559-h.htm#13