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52
SPECIAL REPORT ON "DRAINTESTING,"
(Presented to, and adopted by, the Vestry on May 24th, 1900).
I have to report that there are three methods of testing drains:
1. With water under pressure—the hydraulic or water test;
2. With smoke under pressure—the smoke test;
3. With odorants or chemicals—the smell or chemical test.
The only trustworthy test is the hydraulic or water test, and,
theoretically, such is the only test that ought to be used, whether
dealing with old or new drains. There are, however, many practical
difficulties in the way of systematically carrying out such a
test, e.g., the necessary opening up of the drain in front, when
there is no manhole; the severity of the test, especially when
applied to a length of drainage, etc. Such practical difficulties
have stood in the way of this water or hydraulic test being used
indiscriminately, at least, in connection with old drains, of which
few, if any, would stand the trial, either in Lambeth or elsewhere.
In Lambeth, since I have been Medical Officer, the hydraulic
test is the only one used in connection with new drains, and this
is applied to the drains, not only in sections as they are laid, but
as a whole when completed and filled in. Even with such strict
precautions, however, it is found in practical experience that a
drain which is water-tight when laid, does not necessarily remain
so afterwards for any length of time, at least, when earthenware
pipes are used and are subjected, as they may be, to the cracking
and twisting influences of concrete or cement, to subsidences or
shiftings in the ground, vibrations from railways, and other causes,
etc.