|(a) If the use of the appropriated water is authorized for
multiple purposes, the water right shall contain a special condition limiting
the total amount of water that may be actually diverted for all the purposes
to the amount of the water appropriated.
(b) If a water right has appropriations with different priority
dates, the oldest priority water shall be credited against the water first
used unless the water right expressly provides otherwise or the water right
holder requested the watermaster to count the water use against the junior
portion of the right.