History of the Water Supply Bank

Rental Pool Beginnings

Before the current statutory mechanism was enacted creating an Idaho Water Supply Bank, a rental pool had been employed for many years by the water users in Eastern Idaho. The rental pool allowed entities with surplus storage water to make it available to others who found themselves short in a particular year.

Many canal companies hold natural flow rights with priorities which are adequate to provide a full supply of water except in years of low streamflow. In the good to high runoff years the company finds itself with surplus water. It then must weigh the benefit to be received from renting the storage to another user against the risk that the storage space may not refill during the following season. If the risk is seen to be reasonable, the surplus is made available for use by others.

The first known annual rental pool transfers occurred during the drought period of the 1930s when 14,700 acre feet of water was rented for 17 cents per acre foot in 1932. Then in 1934, 40,000 acre feet of water was rented for 25 cents per acre foot. In the following years the annual rental price increased to 75 cents per acre foot in 1978 with part of the fee going to the entity supplying water to the rental pool and part going to the water district to cover administrative costs.

A Formal Plan

In 1979 the Idaho Legislature formalized the program of annual leases of storage water entitlements. The legislation set into law a 1976 policy recommendation of the state water plan which had called for the creation of a "water supply bank... for the purpose of acquiring water rights or water entitlements from willing sellers for reallocation by sale or lease to other new or existing uses." The responsibility for the water supply bank was placed under the Idaho Water Resource Board.

In 1979 the Water Board appointed the Committee of Nine, which is the water district advisory committee as the local committee to administer the program in the Upper Snake River Basin, an area designated Water District 01. This district covers all of the area of the state served by water from the Snake River from the Wyoming border to the Milner diversion dam near Twin Falls. The river irrigates about 1.2 million acres from natural flows held by private canal companies together with about 4.1 million acre feet of storage space in federal private reservoirs.

In 1988 a second water bank was started, this time in the Boise River drainage basin. This system serves about 300,000 acres of irrigated farmland with natural flow and about 1 million acre feet of storage in three federal reservoirs.

In 1990, a third water bank rental pool was formed encompassing the Payette River drainage. There is also a fourth water bank rental pool which involves the Sho-Ban Tribes.