PROPERTIES OF WATER AND SOURCES OF SUPPLY. 27 



in mind, however, that no matter how this water 

 may be otherwise free from atmospheric pollution 

 (this of course being the case in country districts), 

 there is always an element of danger from a sanitary 

 aspect of fouling of the water by excrement from 

 birds, but except in houses near the sea whence sea- 

 gulls may find their way inland, or houses surrounded 

 by rookeries, this is hardly worthy of much consider- 

 ation. 



