standpoint of both water quantity and 
quality. 
e Surface-water quality has been a 
concern for much of this century. 
Legislation in the early 1970’s targeted 
point sources of pollution. The private 
sector's response and strict 
enforcement of the laws have reduced 
point sources of pollution and created a 
real success story—up to 90 percent of 
our inland surface waters are now 
fishable and swimmable. 
e Various nonpoint sources of 
pollution are the principal sources of 
residual problems where surface waters 
do not meet designated use standards. 
Ground-water quality concerns could 
engender significant changes in 
agricultural practices. Also, water 
management policies may create 
situations Where uses are not 
compatible, such as management of 
water levels in reservoirs without 
regard to effects on fish and wildlife. 
e With regard to fish and wildlife, it is 
estimated that about 80 percent of the 
Nation's flowing waters have 
opportunities to improve water 
quantity, water quality, fish habitat, or 
composition of the fish community. 
However, it is also estimated that some 
two-thirds of U.S. streams have habitat 
adequate for sports fish. 
e In general, water quality has 
improved significantly in the last 
decade, and continued monitoring and 
enforcement of laws and regulations 
should make it even better. 
e Average annual flood damages are 
expected to increase in the future 
mainly due to increased development 
and rising property values on flood 
plains. 
16 
The Water Resource 
The water resource may be viewed as 
moving in a never-ending cycle. Rain 
or other precipitation soaks into the soil 
or runs off the land: water is used or 
stored in reservoirs or aquifers; it 
evaporates or is transpired by 
vegetation and becomes rain again. The 
quality of the resource at each stage in 
the hydrologic cycle is important in 
assessing the status of the water 
resource. 
The quantity of freshwater in rivers and 
streams is largely a function of the 
amount of precipitation falling on 
watersheds. Average annual 
precipitation ranges from a few tenths 
of an inch in some desert watersheds of 
the Southwest to nearly 400 inches in 
some Hawaiian watersheds. About 
two-thirds of the precipitation that falls 
either evaporates directly or is taken up 
by plants and transpired back to the 
atmosphere. The remaining third either 
runs over the soil surface to streams or 
percolates into the soil and moves 
through the soil profile to streams via 
flows of ground water. There is much 
variation around the country in the 
percentage of water that actually ends 
up as part of the Nation’s usable water 
resource. Climate, vegetative cover, 
topography, and soil type all influence 
the type and amount of runoff that 
occurs 1n each geographic area. 
The renewable water supply of the 
coterminous United States amounts to 
about 1.4 trillion gallons per day. The 
available supply is not likely to change 
much in the future, but there is much 
uncertainty in trying to estimate short- 
term supplies because of droughts, 
major storms, and other natural 
phenomena. 
The volume of ground water in storage 
in the upper half-mile of the Earth’s 
crust within the coterminous United 
States has been estimated to be 55 
quadrillion gallons. Not all of this 
water is suitable for human uses. The 
recharge to the ground-water system is 
1 trillion gallons per day. The total 
ground water withdrawn in 1985 
represented about 24 percent of the 
total freshwater withdrawals in the 
United States. The ground-water 
resource situation varies around the 
country, depending, for example, on 
the extent of irrigation and changes in 
ground-water quality. 
Reservoirs provide a means to store 
water when plentiful and use it when 
needed. At present, there are 2,654 
reservoirs and controlled natural lakes 
having capacities of 5,000 acre-feet 
(1.63 billion gallons) or more in the 
United States and Puerto Rico. They 
have a combined storage capacity of 
480 million acre-feet (156.4 trillion 
gallons). In addition, there are at least 
50,000 smaller reservoirs with 
capacities in the range of 500 to 5,000 
acre-feet and about 2 million farm 
ponds used for storage. There remain 
about 750 million acre-feet (244 trillion 
gallons) of potential storage in the 
continental United States where 
building dams is feasible from an 
engineering perspective. Most of the 
cost-effective sites have been 
developed, however, and the Nation’s 
reservoir capacity may be gradually 
approaching the limit of economically 
viable development. 
The quality of water in many major 
streams has improved markedly over 
the past two decades. Laws mandating 
pollution abatement have worked, and 
major point sources of pollution are 
being brought under control. Experts 
