Data Center Water Usage in Ohio: aquifers, OEPA rules, and the Marysville case

How much water does an Ohio data center actually use?

The honest answer is: it depends on the cooling design, and most operators do not publish their figures in detail. Industry estimates published in 2025 put a medium-sized data center (10 to 20 megawatts of IT load) at up to 110 million gallons per year for cooling alone. A hyperscale facility in the 100-megawatt class can consume around 528,000 gallons per day, with the largest facilities reaching 1.5 to 5 million gallons per day in the U.S. average. Google's average data center globally consumes roughly 550,000 gallons per day according to its 2024 environmental report.

For Ohio specifically, the most concrete number on the public record comes from Marysville, where two operating facilities together consume about 10% of the city’s entire daily water supply, according to reporting cited in the Washington Informer's December 2025 review of central Ohio water pressure. That figure is on a small-city baseline (Marysville population is roughly 27,000), but it illustrates the structural problem: data centers are large industrial water consumers being sited inside cities whose water systems were built for residential and commercial demand only.

The Marysville case and central Ohio groundwater

The Mid-Ohio Regional Planning Commission's Central Ohio Regional Water Study, a multi-agency analysis of the region's long-term water needs, has flagged that water and wastewater demand will rise sharply in the coming decades because of the data-center buildout. The study also identifies groundwater subsidence — the gradual sinking of the ground surface from sustained aquifer withdrawal — as a problem that “will become much more serious in the next decade if demands continue unchecked.”

Subsidence is not theoretical. It causes infrastructure damage to streets, sewer pipes, building foundations, and well casings. Once it occurs, it cannot be reversed by simply reducing withdrawal. Ohio's central counties — Franklin, Licking, Madison, Union, and Delaware — sit on this aquifer system.

What Ohio EPA permits govern data center water

Data center wastewater discharges in Ohio are governed by the Ohio EPA's National Pollutant Discharge Elimination System (NPDES) permit framework. In 2025 and 2026, Ohio EPA released a draft General NPDES permit specific to data center facilities — covering non-contact cooling water, cooling tower blowdown, and associated stormwater. Two structural concerns have emerged from the draft as published:

• The draft does not specify nitrate limits among the regulated pollutants. Nitrate migration from data center water cycling has been linked to drinking-water concerns in other states.
• The permit relies on existing antidegradation standards, which under Ohio rules permit lowering of water quality “when deemed necessary to accommodate important social or economic development.” In practice, regulators are signaling that some degradation may be acceptable to support data center growth.

For residents, this means that the threshold for permit denial is low and that the practical defense against water-quality impact runs through the public-comment phase of individual project permits, not through the general NPDES permit itself.

Cooling design matters more than facility size

A 100-megawatt data center using direct evaporative-free air cooling may use water only roughly 3% of the year, in the hottest summer days. Prologis has filed this design specification for Project Mila in Trenton (Butler County). By contrast, a similar facility using cooling tower evaporation may run continuously and consume 100× to 300× more water annually.

This is why the Miami Valley Conservancy District's Mark Ekberg told a Shelby County town hall in March 2026 that some data centers can consume up to 300 gallons of water per minute — that figure is the cooling-tower scenario, not the air-cooled scenario. Whether a specific Ohio project poses a major water risk depends on which cooling design is actually built, and that is rarely disclosed in detail before approval.

Where Ohio data centers get their water

Most Ohio data centers draw from municipal water systems, not from private wells or direct surface water. This means the cost of expanding water-treatment capacity falls on the municipality and is paid by all ratepayers, not just the data center customer — unless the project's development agreement specifies otherwise. Sidney's Project Galaxy agreement (Shelby County) is one example where the city has stated its water system has “sufficient capacity and multiple sources” without publishing peak-load modeling. The Marysville and New Albany cases are examples where capacity was expanded over years to accommodate the cluster.

For rural and semi-rural Ohio counties — Brown, Adams, Clermont, Preble — the water question is sharper because municipal capacity is smaller and surrounding agricultural land relies on private wells. The Ohio Farm Bureau's Jordan Hoewischer has recommended residents near proposed data centers establish baseline well-water testing every 2 to 6 months, “in case something ever does happen.”

What the 25-megawatt threshold means

The Ohio Constitutional Amendment now in active signature collection through July 1, 2026 — coordinated by Ohio Residents for Responsible Development — would prohibit new data centers above 25 megawatts of peak monthly load. Twenty-five megawatts is roughly the threshold at which a data center crosses from being a manageable industrial customer into a hyperscale facility whose water and electrical demand exceeds typical municipal capacity. Maine adopted a similar 20-megawatt threshold in its 18-month moratorium. Most of the Ohio projects covered on this site — Project Mila (250 MW), Bristolville 25, Project Galaxy, Cosgray Road — would be banned under the proposed amendment.

What residents can do during permit review

The Ohio EPA's NPDES permit process includes a public-comment period for each individual data center project after the general permit is in force. Residents can submit written comments objecting to specific water-use volumes, cooling-method choices, or wastewater discharge plans. The county-level commissioner conversation typically happens earlier, during zoning approval; the state-level water permit is a second window.

For projects that draw from municipal water (most Ohio data centers), the relevant body is the city council or village trustees, not Ohio EPA. The city's existing water-supply agreement with the data center is part of the public record under Ohio's Sunshine Law (R.C. 149.43), even when the development agreement itself was negotiated under NDA.

• Washington Informer — Ohio faces water crisis amid rising data center growth (December 2025)
• Ohio House — Christine Cockley — More than electricity: data centers' water use scrutinized (August 2025)
• Mid-Ohio Regional Planning Commission — Central Ohio Regional Water Study
• Ohio EPA — Draft General NPDES Permit for Data Center Facilities
• Ohio Environmental Council — data center water concerns
• EESI / npj Clean Water — Data Centers and Water Consumption (industry baselines)
• WHIO — Miami Valley Conservancy District Mark Ekberg (300 gpm figure)

• Data centers and your Ohio electric bill — AEP’s 85% tariff, PJM capacity, BTCR riders
• Data center noise in Ohio — cooling-tower hum, generator testing, decibel limits
• Data centers and your property value — what GMU’s study found, what Mansfield residents say
• Is there a data center near my home? — how to check your Ohio county
• Data center health risks in Ohio — diesel emissions, fuel cells, air quality