ed a mass of data which will be welcomed
by engineers engaged in water purification work, because complete
operating records form a substantial basis for improvement in the
art, and are often the inspiration for interesting discussions and
the exchange of experiences of different observers whose views are
mutually appreciated.

Recent tendencies in filtration engineering have been largely in the
direction of reducing the cost of operation. A comparison of the
operating costs of the earlier American plants of about a decade
ago, with those here presented of the Washington plant, is very
gratifying to those who have been intimately connected with the
latter work. Through perfection in design and reasonable care in
operation, the cost of filter cleaning, which is a very considerable
part of the total cost, has been reduced to an unusually low figure,
without any sacrifice in efficiency, and in the interests of the
public health.

Table 14 shows that, from the first year, there has been a
progressive increase in the total cost of operation per million
gallons filtered, but this has not meant an increase in the annual
total expenditure. The largest percentage of increase in any item
has been in "Care of Grounds and Parking," and covers much-desired
landscape improvements. Aside from this, the principal factor
affecting the table of costs has been the reduction in water
consumption in the District of Columbia. Nothing pertaining to this
reduction has produced any corresponding reduction in the force
required for the maintenance and operation of the filtration plant,
office and laboratory, and pumping station, though probably there
has been some reduction in filter cleaning. Obviously, then, the
total cost per million gallons would increase.

This decrease in consumption has been brought about by the
elimination of waste in the distribution system, which is not in the
same department as the filtration plant, but with regard to which a
word may not be amiss in connection with this discussion.

The Washington Aqueduct was built half a century ago on lines which
at that time were considered extraordinarily generous. Until
recently, therefore, there has been no occasion for concern over the
high rate of consumption. During recent years, however, the use and
waste of water have increased, reaching a climax under unusual
conditions in the winter of 1904-05. The maximum capacity of the
aqueduct system is about 90,000,000 gal. T