been, since the laws providing for them are comparatively recent and 
the time for them to have been abandoned is short. 
Certificates or licenses representing rights acquired in accord- 
ance with permits issued by States and as the results of adjudica- 
tions made by State boards or officials and based on surveys made 
and testimony collected by State officials are the best documentary 
evidence of the possession of rights which are likely to be supplied 
by streams in average years, since they are based on proof submitted 
to a State board or official whose duty it is to protect the public and 
are usually issued after inspection by those officials; court decrees 
and certificates rank next ; while permits from State boards or offi- 
cials and copies of filings in county or State offices rank last. 
The preceding discussion may create the impression that there are 
no good titles to the use of water, but that is not the case. The 
point is that documentary evidence alone is not sufficient to establish 
either the existence of a water right or its value. Documentary evi- 
dence must be backed by evidence of the existence of a water supply 
in excess of the demands of prior rights. This involves the study 
of records of stream flow and of existing use. If a stream supplied 
continuously a given quantity of water, and each holder of a right 
continuously used all the water to which he is entitled, the determi- 
nation of the value of a right would be the simple matter of adding 
the amounts of all the prior rights and comparing the sum with the 
total supply of water. But neither the total supply nor the demand 
made on that supply is uniform. The flow of any stream varies 
from hour to hour, from day to day, and from season to season, while 
the demand made by any one user may vary in the same way, so that 
the probability of receiving water under any right when there is not 
enough water for all rights is extremely hard to determine. On the 
same stream there will be early rights whose holders can get water 
whenever they need it, rights whose holders usually get water as 
they need it, and other rights whose holders get water only in flood 
season — with all degrees between these extremes. 
In States having water commissioners, these officials keep records 
of the dates when each ditch received water and how much it 
received. These records, covering a series of years, will disclose 
what ditches have good rights and whether there is water in any 
source beyond the demands of existing rights. Where such records 
do not exist, it is usually possible to learn from local disinterested 
persons what ditches receive a good supply, what ditches ordinarily 
are short of water, and whether, in ordinary seasons, there is more 
water than is demanded by existing rights. A prospective pur- 
chaser of a water right should look carefully into both the docu- 
