Published
Between 85 and 212 degrees, Idaho stops calling it a water well
There is a temperature band where the rules change name
A well that returns warm water is not just a well with a number attached. Between two temperatures, Idaho reclassifies the whole project:
“Drillers constructing low temperature geothermal resource wells (bottom hole temperature more than eighty-five (85) degrees Fahrenheit and less than two hundred twelve (212) degrees Fahrenheit) must be qualified under the Well Driller Licensing Rules.”
— IDAPA 37.03.09 §030.01, construction of low temperature geothermal resource wells and bonding (effective 3-18-22; amendments current through the 7-1-25 docket). Retrieved 28 September 2026
More than 85°F and less than 212°F at the bottom of the hole — that is the band, and it is measured where the truth is: downhole. The owner or well driller must provide the bottom-hole temperature data, but the Director may make the final determination based on the information available. The driller must be qualified under the Well Driller Licensing Rules — the license is the floor, not the ceiling. And the ordinary rules still apply underneath: everything in the standard construction rule carries over except where Rule 30 modifies it. The whole point of the modifications is one sentence in the rule’s own opening: the resource must be protected from waste due to lost artesian pressure and temperature.
The prospectus: approval before anything touches the hole
Where low temperature geothermal resources are known or anticipated, a drilling prospectus must be submitted to and approved by the Director prior to the construction, modification, deepening or decommissioning of the well (7-1-25) — and the well owner and the well driller are both responsible for the prospectus and the construction that follows it. Repairs are not a loophole: the driller must submit a prospectus for review and approval prior to the repair or modification of such a well as well (3-18-22). The drilling permit still rides on top of all of it.
The owner posts the bond
This is the rule’s quiet headline: the owner, not just the driller, files money with the state. Under Section 42-233, Idaho Code, the owner of a low temperature geothermal resource well must file a surety bond or cash bond of not less than $5,000 nor more than $20,000, payable to the Director, before constructing, modifying or deepening the well after July 1, 1987 (3-18-22). The bond is kept in force for one year following completion of the well — or until released in writing by the Director, whichever occurs first.
| The well | The owner’s bond |
|---|---|
| Artesian low temperature geothermal resource well | $5,000 |
| Flows at land surface | $10,000 |
| Flows, with a bottom hole temperature of 140°F or more | $20,000 |
The tiers are the rule’s own (7-1-25), and the Director may decrease or increase any of them where well construction or other conditions merit it. Heat plus flow is what the price climbs on.
Casing and conductor built for pressure
- Steel casing that meets or exceeds the permanent-casing minimums of Rule 25, Subsection 025.04 goes in every well — with a more rigid collapse-and-burst standard available as depth or pressures dictate.
- Drilled where existing wells are known to flow at land surface: a minimum of 40 feet of conductor pipe, set and sealed its entire length, to anchor the wellhead control devices (7-1-25).
- Where artesian pressure is encountered: casing installed from 12 inches above land surface, sealed with approved seal material into the overlying confining strata of the thermal aquifer.
- The last casing string may have to be flanged for a valve or blow-out prevention equipment at the Director’s option — and the Director may require gate valves or annular blow out prevention equipment outright, to prevent an uncontrolled blow out of drilling mud and geothermal fluid.
The seal: cement, from the bottom up, left alone
Heat changes the grout. For wells with a bottom hole temperature greater than 140°F, cement or a cement grout mixture is required — placed from the bottom up through the casing, tubing or a tremie pipe, and then undisturbed for a minimum of 24 hours, or as long as curing needs (7-1-25). The rule also budgets generously for the unknown shape of the hole:
- Caliper log run: an additional 25 percent of seal material on site, ready for mixing.
- No caliper log: an additional 100 percent of the calculated volume on site, ready for placement.
- No return at the surface after circulating everything on site: the Director decides whether remedial work is needed to keep fluids from migrating around the bore.
Retiring a warm well is its own engineering
Decommissioning requires written approval from the Director before any procedure begins (7-1-25). Then the seals, in order:
- All mixed grout seal material pumped into the hole through drill pipe or tubing; all open annuli filled with approved seal material.
- 100 feet of seal straddling each aquifer boundary — fifty feet above and fifty feet below the zone where the casing or well bore meets the upper boundary of each ground water aquifer.
- 100 feet straddling each drive shoe or guide shoe on all casing, including the bottom of the conductor pipe.
- A surface plug from 50 feet below the top of the casing to the top of the casing.
The point of all that depth is the same point behind the owner’s repair-and-decommission duty: a warm, pressurized hole left half-sealed is a fountain waiting for a fault line — and an uncontrolled flowing well is a crime, not a maintenance item.
If the ground you are buying might run warm
- Ask what the neighboring wells found — their driller’s reports are permanent public records, temperatures included.
- Before signing a drilling contract, confirm the prospectus is approved, not merely drafted.
- Check the bond tier against the well you actually expect — artesian, flowing at the surface, or flowing and hot.
- If the well exists already, ask whether the old owner’s bond was released in writing or simply forgotten.
- Warm ground moves the septic plan too — bring both files to (208) 656-1467.
Common questions
What counts as a low temperature geothermal well in Idaho?
A well with a bottom hole temperature more than 85 degrees Fahrenheit and less than 212 degrees Fahrenheit. The owner or well driller must provide the bottom hole temperature data, but the Director may make the final determination based on the information available.
Who is allowed to drill a warm-water well?
A driller qualified under the Well Driller Licensing Rules - the licensing page on this site covers what that credential takes. All such wells must also be built so the resource is protected from waste due to lost artesian pressure and temperature.
What is a drilling prospectus?
The plan that must be submitted to and approved by the Director before the construction, modification, deepening or decommissioning of any low temperature geothermal resource well. The well owner and the well driller are both responsible for it.
How big is the owner's bond on a warm well?
$5,000 for an artesian low temperature geothermal well; $10,000 if it flows at land surface; $20,000 if it flows with a bottom hole temperature of 140 degrees Fahrenheit or more. The Director may decrease or increase the amounts where construction or conditions merit.
How long does the owner's bond stay in force?
One year following completion of the well, or until released in writing by the Director - whichever occurs first.
What casing does a warm well need?
Steel meeting or exceeding the Rule 25 permanent casing minimums. Where existing wells are known to flow at land surface, a minimum of 40 feet of conductor pipe set and sealed its entire length; where artesian pressure is encountered, casing from 12 inches above land surface sealed into the overlying confining strata of the thermal aquifer.
When is cement required instead of ordinary seal material?
For wells with a bottom hole temperature greater than 140 degrees Fahrenheit - placed from the bottom up through casing, tubing or a tremie pipe, and left undisturbed a minimum of 24 hours or as long as adequate curing needs.
Why must extra seal material sit on site?
Volume insurance for a hole whose true shape is uncertain: 25 percent extra ready if a caliper log was run to measure it, and 100 percent extra if it was not. If circulating the material produces no return at the surface, the Director decides whether remedial work is required.
How is a warm well decommissioned?
Only with written Director approval before any procedure begins - then grout pumped through drill pipe or tubing, 100 feet of seal straddling each aquifer boundary (50 feet above and below), 100 feet straddling each drive or guide shoe, and a surface plug from 50 feet below the casing top to the top.
Do repairs to a warm well need approval too?
Yes. The well driller must submit a drilling prospectus to the Director for review and approval prior to the repair or modification of a low temperature geothermal resource well.