262 
IOWA ACADEMY OF SCIENCE Voi.. XXVII, 1920 
TABLE NO. 2. S. U. I. — SWIMMING POOLS 
January 27, 1916 — March 31, 1920 
Women 
Men 
FieeEd 
Emptied 
D'ays 
FielEd 
Emptied 
D'ays 
1-21-16 
5-19-16 
119 
1-21-16 
5-27-16 
127 
5-21-16 
8-24-16 
95 
5-28-16 
8-24-16 
88 
9-21-16 
12-21-16 
91 
9-25-16 
12-21-16 
87 
1-6-17 
4-4-17 
88 
1-5-17 
4-4-17 
89 
4-9-17 
6-12-17 
64 
4-9-17 
6-9-17 
61 
6-19-17 
8-25-17 
67 
6-21-17 
8-26-17 
66 
9-28-17 
12-22-17 
85 
9-25-17 
12-22-17 
88 
1-6-18 
1-19-18 
13 
1-7-18 
1-19-18 
12 
2-22-18 
6-5-18 
103 
2-22-18 
3-28-18 
36 
6-17-18 
l8-31-18 
75 
4-3-18 
6-7-18 
65 
1-28-19 
6-13-19 
136 
6-21-18 
8-30-18 
70 
6-18-19 
8-30-19 
73 
1-22-19 
3-21-19 
58 
10-9-19 
11-28-19 
51 
3-25-19 
6-13-19 
80 
1-11-20 
3-25-20 
74 
6-18-19 
7-25-19 
37 
7-30-19 
8-30-19 
31 
10-6-19 
11-28-19 
53 
1-7-20 
2-12-20 
36 
2- 17-20 
3- 31-20 
3-26-20 
38 
Since the condition of the pool water is dependent upon the 
contamination introduced by the bathers and the natural multi- 
plication of bacteria as well as upon the amount of purified 
water returned to the tank and the degree of purification, it has 
been thought best to take all samples after the pool has been used 
for the day so as to have samples representing the worst con- 
dition of the pool. It is obviously undesirable to take the effluent 
from the filters as a representative sample because that represents 
the purified water rather than the pool water itself. A small 
quantity of practically sterile water is naturally not able to im- 
prove the quality of the pool water to the same extent as a large 
volume of water not quite so thoroughly treated. 
There is no agreement upon the degree of purity necessary in 
the water of swimming tanks, although it would be generally 
accepted that the more nearly the water approached the purity 
of drinking water, the better. But there is no very general agree- 
ment as to the degree of purity which a water must have to pass 
into the classification of drinking water. Perhaps the United 
States Treasury Department Standard of 1914, for water sup- 
plied to passengers by common carriers in interstate traffic, is the 
most generally recognized standard. It requires that the water 
shall show less than one hundred bacteria per c.c. on agar at 37° C. 
after 24 hours incubation and also that it shall show not more than 
one positive confirmed test for B. coli out of five 10 c.c. plantings 
