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The Future of Idaho's Water

During this legislative session, we supported legislation that updates a critical boundary in Idaho’s Eastern Snake Plain Aquifer (ESPA). This boundary, also known as Rule 50, defines an area of common groundwater and creates an administrative border for the Department of Water Resources to administer water rights conjunctively. The current line reflects the best available science in the mid-1990s. 

Today, we know a lot more about the ESPA. We can see in more detail how water moves in this complicated system. Science now makes a strong case that Rule 50 needs to expand to include all groundwater users within the ESPA and the tributary basins outside the existing border to improve how we administer water rights.

In 1992, the Idaho Supreme Court directed the department to adopt conjunctive management. It recognizes the connection between surface water and groundwater systems. In addition to runoff from our snowpack, the aquifer also provides river flows in some reaches of the river. When this system gets out of balance, it can impact whether surface water users with senior rights receive their portion of water.

The department adopted the current conjunctive management rules in 1994. Any water users within Rule 50 fell under the conjunctive management rules, and their rights were administered in priority. Over time, Idaho’s hydrologists improved the groundwater model to include the entire ESPA and started tracking how tributary basins fed water into the larger river system. Any activity that affects groundwater levels may also contribute to how much water eventually flows to surface water users downstream. Tracing how water moves in Idaho matters because we apply prior appropriation to water in our state.

Also known as “first in time, first in right,” we administer water rights based on seniority. Older water rights trump junior water rights. In most parts of the state, groundwater rights are junior to senior rights. Technology for groundwater pumping wasn’t widely available until decades after surface rights were claimed. Conjunctive management ensures that the department administers surface water and groundwater rights in line with prior appropriation.

Since 2005, ESPA surface and groundwater users have engaged in multiple administrative proceedings. These actions include water delivery calls made by senior surface water users. A water call happens when a senior water user isn’t receiving an adequate water supply.   

All water users have spent significant time and money on administrative and legal proceedings to resolve delivery calls. Every year, the department reviews the available water supply and works with water users to protect water rights. In a year with a short supply, junior water users may be called upon to mitigate their usage to prevent harm to senior users through voluntary pumping reduction, recharging the aquifer, or buying storage water. 

But the department can only protect and administer what the law and rules allow. That’s why it’s critical to expand the current Rule 50 boundary to match the updated model for the ESPA. This update doesn’t come with automatic changes. The department director must establish water districts in the tributary basins, notify water users, and hold public hearings before any new administrative action. Only then may the director issue an order, which the courts can review.

We have friends and family on both sides of the boundary line. Reaching this point required compromise and hard work. But it’s an issue we need to address to ensure a sustainable future for Idaho’s water. 


Sen. Van Burtenshaw, Rep. Rod Furniss, and Rep. Jerald Raymond represent District 31 (Clark, Fremont, Jefferson, and Lemhi counties). Sen. Julie VanOrden represents District 30 (Bingham and Butte counties). Rep. Stephanie Mickelsen represents District 32 (Bonneville County).