Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1891-05-04
OUR MAIL POUCH.
overed Reservoirs Worth Considering.

Covered Reservoirs Worth Considering.
To the Editor of The Dispatch:
The subject of your article on covered reser-
voirs is of peculiar interest; and is one shat
is being brought more and more into promi
nence in this country as well as in Europe. a
number of covered reservoirs having already
been buift here. The principal reason for COW
ering reservoirs has been. heretofore. to pre-
vent their detilement by SCOT, smoke dust. OBJ
noxious gases and the various kinds of house
bold waste and garbage that so often find their
way into most unexpected and unfit places.
This condition frequently obtains in our cities
where distribution reservoirs can often only be
constructed to advantage in the close proxim-
ity to fruitful sources of pollution of this
character. For somewhat similar reason
numberNof towns in the far West and else where
have found IL a matter Of economy to cover
their reservoirs in order TO prevent the deposit
of sand blown in by high winds passing over
dry and sandy soil Again, in hot climates it is
done to keep the supply OF water cool, and in
ice, which latter is sometimes a source of
serious injury to reservoirs and of annoyance
in cioggng the pipe inlets. The recent failure
OF an iron stand-pipe at Defiance. o.. is good
illustration of the destructive capacity OF this
agent
But the more recent as well as the more i'm
porrant application of roofs to distribution
reservoirs is based on the effect of light on
those minute plants known as algR, which are
almost universally present in our streams and
other surface waters, and which, under favor
rapidity, so that in the course of few hours
large lake may become, as it were, carpeted
with thick covering of them. So common
source OF annoyance is this to many OF our
cities using surface waters, that for the past
few years many of our water boards and boards
of health have directed their best efforts to its
abatement resulting in marked advance in
our knowledge of tho manner in which these
organisms may work for our good or ILL.,
In general it may be said that this source of
pollution has Deen found simply offensive and
that there results no perceptible harm in TAX
ing water thus polluted into the system. But
under certain conditions the taste and odor
impaired to the water is SO disagreeable, to say
the least as to make 1t unfit for use.
In what direction shall relief be sought? for
evidently any attempt at removal by straining
is but temporary if not useless. So far, there
are two perfectly practicable methods in use.
First, that of aerating the water, either by
pumping air into the MAINS as was done by
DIR. A. r. Leeds. at Hoboken, N. j., and else
where, or by agitation (by letting the water
fall through sieve or pass through Jet into
the reservoir, or otherwise), by which means
the oxygen absorbed from the air has been
found to destroy the organisms and remove the
offensive odor and taste. Secondly, by keeping
the water under cover and away from the sun
light. This has been proved very efficacious in
a water supply near Boston on which the ex-
pertinent was tried some two or three years
ago, and after due investigation the explanation
was shown to be as follows: Alg8 are
divided into two great classes-those con-
tanning chlorophyl. or the green color
ing matter of plants (alge proper, and
those in which it is absent As with plants of
higher orders sunlight is found requisite to
develop this green coloring matter. and while
those plants which do not contain it may live
in the dark, yet they do depend for their sus-
tenance on those plants which do contain
chlorophyl. In other words, they are parasitic,
and cannot assimilate inorganic matter direct
ly. Thus, we see that when sunlight Is shut off
from reservoir containing the green alg8,
not only are these destroyed, but also the re-
manning or parasitic ones. and in this way the
water is protected from either form of vege-
table organism.
1t is, perhaps with reference to this more i'm
portant phase of the question that many of our
troublesome water supplies will have to be
treated in the future. A.
SCoTTDALE, May 2.