Does a deeper well mean better water?

Depth and yield do not move together

If deeper meant better, the deepest counties in Idaho would also be the highest-yielding. They are the opposite.

Kootenai County has the deepest median well in the state at 380 ft, and a median yield of 15 gpm. Canyon County reports the highest median yield at 50 gpm from wells with a median depth of 140 ft — less than half as deep.

Depth is a function of how far down a productive layer sits. A deep well is evidence the driller had to go a long way to find water, which is a cost, not a quality.

What depth does change

Deeper water is often older and better protected from surface contamination, which is a genuine advantage against things that come from the surface — septic systems, fertiliser, livestock.

It can also pick up more dissolved minerals from longer contact with rock, which is a treatment question rather than a safety one.

Neither of those is predictable from depth alone. The only thing that tells you what is in a particular well is a laboratory test of that well.

The cost runs the other way

Every extra foot is billable. At published Idaho rates, the difference between a median well in Lemhi County and one in Kootenai is $2,300–$4,000 against $13,300–$22,800 — for the borehole alone, before casing or a pump.

Depth to water matters too: the further water sits below the surface, the more pump you need and the more it costs to run every month for the life of the well.

So what should you ask instead?

• What depth do wells near this parcel actually reach, and how much do they vary?
• What yield did they report, and is that enough for what I plan to do here?
• What has a laboratory test of this specific well found?