Well Water in Delaware County, Ohio

Delaware County · Population ~220,000 · Aquifer: Glacial Drift / Delaware Limestone

Hardness: 300-500+ PPM (17-29+ gpg) — Very Hard to Extremely Hard

Delaware County is one of the fastest-growing counties in Ohio and one of the wealthiest. The northern half is still heavily rural, and thousands of homes in places like Sunbury, Powell's outskirts, and Galena rely on private wells. The Delaware Limestone beneath produces some of the hardest water in the state.

The Delaware Limestone

Much of Delaware County sits atop the Delaware Limestone — a Devonian-age carbonate formation that dissolves readily in groundwater. The result is water that is extremely hard, often exceeding 500 PPM (29 grains per gallon).

This isn't just a nuisance. At these hardness levels, water heaters fail years early, pipes scale shut, and laundry comes out stiff. A water softener isn't optional — it's a necessity.

Hydrogen Sulfide

The "rotten egg smell" is one of the most common complaints from Delaware County well owners. Hydrogen sulfide gas is produced by sulfate-reducing bacteria in the limestone aquifer. It's not typically a health hazard at the levels found here, but it makes the water unpleasant to drink and can tarnish silver and copper fixtures.

Treatment options include aeration systems, oxidation filters, or activated carbon. For mild cases, a whole-house carbon filter may be sufficient.

Agricultural Impact

Despite the suburban growth in the south, most of Delaware County is still farmland — corn and soybeans dominate. Nitrate contamination from fertilizer application is a real concern for wells near active agricultural fields, especially shallow wells in glacial drift.

The EPA maximum contaminant level for nitrate is 10 mg/L. Wells should be tested annually, and more often if you're adjacent to row crops.

What to Test For

Every Delaware County well should be tested for bacteria, nitrates, hardness, iron, manganese, and pH. If you notice a sulfur smell, add hydrogen sulfide to the panel. The Delaware General Health District regulates private water systems and can provide guidance on testing labs.

See our testing guide for labs, costs, and county health district contacts.

Every well is different. Two wells on the same street can produce completely different water. The data on this page reflects documented conditions in the Delaware County area, but the only way to know what's in your water is to test it.

Sources

  • Ohio DNR — Delaware County Groundwater Resources
  • USGS — Water Quality in the Great and Little Miami River Basins
  • Delaware General Health District — Private Water Systems
  • Ohio EPA — Ambient Groundwater Quality Monitoring