How deep are water wells around Conroe?

The layers, from the top down

Montgomery County sits on the Gulf Coast aquifer system. A 1971 Texas Water Development Board and U.S. Geological Survey report on the county, still the most detailed one we could open, lists the water-bearing layers in this order: the Chicot aquifer at the top, the Evangeline below it, a clay layer called the Burkeville aquiclude, then the Jasper aquifer in an upper and a lower part, and the Catahoula Sandstone at the bottom.

The state's own summary describes the Gulf Coast aquifer as beds of sand, silt, clay and gravel, with up to 1,300 feet of sand in the north of the aquifer and fresh water averaging about 1,000 feet of saturated thickness. That is a thickness, not a depth to water, and it is why the same county can have shallow wells in one spot and very deep ones in another.

Why depth varies from one road to the next

The report gives each layer a tilt: the base of the Chicot dips about 10 feet per mile, the Evangeline about 40, the upper Jasper about 50, the lower Jasper about 85 and the Catahoula about 90. A layer that sits near the surface in one part of the county is hundreds of feet down some miles away, and the thin top layer pinches out in places.

Which layer a household well uses is a choice. The 1971 report says that in 1966 almost all of the county's rural domestic and livestock water came from the Evangeline and the upper Jasper. Today the district keeps different spacing rules for each group, and its resources page calls the Catahoula the county's alternative water source. A well must be completed in only the aquifer named in its application, according to the district's rules, so the choice is made on paper before drilling.

Depths recorded for actual county wells

The U.S. Geological Survey publishes records for monitoring wells in Montgomery County. These are observation and public-supply sites, not typical homes, so do not read them as the depth your well will need. They do show how far apart the layers sit.

• An Evangeline aquifer well in the south of the county is 718 feet deep.
• Jasper aquifer wells recorded in the south and center of the county are 1,500, 1,576 and 1,650 feet deep.
• A Catahoula Formation well at about the latitude of Willis is 2,940 feet deep, drilled in a 3,400-foot hole.

The north and west of the county

In the north, around Willis, and in the west, near the town of Montgomery, the same report finds that the Catahoula holds fresh water in places but, where it does, is generally overlain by slightly or moderately saline water. Its maximum fresh-water sand thickness in the Catahoula, 160 feet, is about 5 miles northwest of Willis, and its thickest slightly saline sand, 200 feet, is northwest of the town of Montgomery. See the Willis and Montgomery area pages for what that means for owners there.

How to look up wells near you

A written well report is the best depth estimate you can get. A driller who has worked your road will usually know the layer too. The new water well page lists what to ask, and the cost guide shows why every extra hundred feet changes the price.

• Lone Star Groundwater Conservation District runs a public well map showing registered and permitted wells in the county. The district's home page links to it.
• Wells drilled after 2002 are filed in the Texas Water Development Board's Texas Well Reporting System. Older reports are held by the Texas Commission on Environmental Quality, according to the state licensing agency.
• Texas A&M AgriLife points owners to the TWDB Groundwater Database, the TCEQ water well report and local districts for historical records, and says to keep a file on each well.
• Ask your neighbors what their driller's report says about total depth and the layer used. A report lists the depth and thickness of each stratum.

Common questions