ns of capacity...| 20,600 | 14,000 | 9,000 | 6,500
----------------------+------------+------------+------------+------------
Cost per million | | | |
gallons of average | | | |
daily output..........| 24,400 | 17,500 | 12,000 | 10,000
----------------------+------------+------------+------------+------------
Capital charges and | | | |
depreciation at 6% on | | | |
cost per million | | | |
gallons...............| 4.00 | 2.87 | 1.97 | 1.64
----------------------+------------+------------+------------+------------
Operating expenses, | | | |
the same at all | | | |
rates.................| 1.00 | 1.00 | 1.00 | 1.00
----------------------+------------+------------+------------+------------
Total cost of | | | |
filtering, excluding | | | |
pumping, storage, and | | | |
all auxiliaries.......| 5.00 | 3.87 | 2.97 | 2.64
----------------------+------------+------------+------------+------------
Relative cost.........| 1.29 | 1.00 | 0.77 | 0.68
======================+============+============+============+============

When the costs of pumping, pure-water reservoirs usually necessary,
etc., are taken into account (which add equally to the cost at all
rates), the cost of filtering will vary less with the rate than is
indicated.

The effect of rate on cost, as calculated in Table 23, and also the
percentages of the bacteria of the raw water found in the effluents
by the author and by Mr. Clark, are shown on Figure 10.

Considering all these results together, and also all the other
evidence known to the writer bearing on this point, it seems clear
that filters are not as sensitive to changes in rate, within
reasonable limits, as has been frequently assumed; but, on the other
hand, there is usually a substantial increase in the percentage of
bacteria passing through a filter with increased rate.

Filters furnish relative, not absolute, protection against
infectious matter in the raw water. The higher the ba