A YEAR IN SCIENCE 



matters which nature must eliminate. Through the 

 lungs and kidneys, the average person excretes about 

 four pints of water per day. 



Thus the demand for fresh water is constant. This 

 is not entirely supplied by the water we drink, for the 

 greater part, by weight, of many of our solid foods is 

 water. Thus potatoes contain 78% water, milk 85% , 

 beef over 50%, tomatoes and asparagus 94%, while 

 some fruits, such as strawberries and watermelons, are 

 over nine-tenths water. Bread probably contains as 

 little water as any of our common foods, and it is about 

 35% water. 



Dangers in water. Pure water is practically un- 

 known. Owing to its solvent action, all water that 

 passes through the soil carries more or less mineral 

 substances or gases in solution. The peculiar taste or 

 odor of the water from a mineral spring is due to the 

 substance the water holds in solution. Even rain 

 water, which is water that has been evaporated from 

 the surface of the earth into the higher atmosphere and 

 then sent back again, is not pure. In its passage 

 through the air it carries along with it the small dust 

 particles it encounters and it probably absorbs some 

 gases from the air. The substances thus far mentioned 

 are not necessarily harmful. Indeed, the dissolved min- 

 erals are necessary to plant and animal life. ^But 

 bacteria are found practically everywhere, on the sur- 

 face of the earth and in the air. It is when the harm- 

 ful bacteria get into drinking water that it becomes a 



