What water 
is purest? 
32 WORLD OF INVISIBLE LIFE 
There are few alto in'deep well-water, coming 
from a depth of a hundred feet or more, for 
soil microbes are not found far below the sur¬ 
face of the earth. All waters near the surface 
of the earth, or waters open to the air contain 
them. But they are fewer in standing waters, 
such as lakes and ponds, than in flowing 
streams. We usually think that river water is 
purer than that of ponds or lakes, but this is 
not true. The reason is that rivers and brooks 
gather the microbes from the earth which is 
washed into them by rains, and carry them 
along. The rivers are the great drain-pipes for 
the country and the farther they go the more 
microbes they contain. But when water stands 
still, as in lakes and ponds, the microbes, being 
a little heavier than water, settle to the bottom 
in a few days; so after a time the water becomes 
far purer than any river. Rivers into which 
sewage or other decaying matter is emptied, of 
course, contain many more microbes than any 
other, and in such water we find the most dan¬ 
gerous, germs; those cast off by sick people. 
