Groundwater vs. surface water, state by state
At a glance
Nationally, 90% of active public water systems draw mainly on groundwater and 9.6% on surface water, counting purchased supplies. Wisconsin relies on groundwater most (99% of its systems) and Kentucky least (31%). In Kentucky, more systems use surface water than groundwater.
Share of each state's active public water systems whose primary source is groundwater (including purchased groundwater) vs. surface water.
Dataset updated . Source: EPA SDWIS/ECHO, refreshed quarterly.
| # | State | Groundwater share | Groundwater systems | Surface-water systems | All systems |
|---|---|---|---|---|---|
| 1 | Wisconsin | 99.4% | 10,993 | 63 | 11,056 |
| 2 | Mississippi | 98.8% | 1,119 | 14 | 1,133 |
| 3 | Minnesota | 98.5% | 6,367 | 98 | 6,465 |
| 4 | Delaware | 98% | 484 | 10 | 494 |
| 5 | Florida | 97.9% | 5,088 | 109 | 5,197 |
| 6 | Nebraska | 97.4% | 1,194 | 32 | 1,226 |
| 7 | Maryland | 97.3% | 2,912 | 79 | 2,992 |
| 8 | New Hampshire | 97.3% | 2,384 | 66 | 2,450 |
| 9 | Indiana | 97.2% | 3,857 | 112 | 3,969 |
| 10 | Michigan | 96.9% | 10,269 | 330 | 10,599 |
| 11 | Maine | 96.3% | 1,793 | 69 | 1,862 |
| 12 | Connecticut | 96.2% | 2,273 | 90 | 2,363 |
| 13 | Idaho | 95.9% | 1,880 | 81 | 1,961 |
| 14 | New Jersey | 95.5% | 3,339 | 157 | 3,496 |
| 15 | Arizona | 95.3% | 1,686 | 83 | 1,769 |
| 16 | Washington | 94.2% | 4,432 | 270 | 4,705 |
| 17 | Rhode Island | 93.8% | 436 | 29 | 465 |
| 18 | Pennsylvania | 93.2% | 6,727 | 490 | 7,217 |
| 19 | Vermont | 93% | 1,262 | 95 | 1,357 |
| 20 | New Mexico | 92.8% | 1,081 | 84 | 1,165 |
| 21 | Hawaii | 92.6% | 126 | 10 | 136 |
| 22 | Ohio | 92.4% | 3,561 | 293 | 3,854 |
| 23 | Louisiana | 92.3% | 1,035 | 86 | 1,121 |
| 24 | Iowa | 92.2% | 1,685 | 143 | 1,828 |
| 25 | Missouri | 91.9% | 2,704 | 239 | 2,943 |
| 26 | New York | 91.3% | 7,459 | 695 | 8,167 |
| 27 | North Carolina | 90.9% | 4,623 | 463 | 5,087 |
| 28 | Georgia | 89.9% | 2,134 | 241 | 2,375 |
| 29 | Virginia | 88.8% | 2,148 | 272 | 2,420 |
| 30 | Montana | 88.6% | 2,106 | 272 | 2,378 |
| 31 | Nevada | 88.2% | 567 | 76 | 643 |
| 32 | Oregon | 87.5% | 2,220 | 316 | 2,536 |
| 33 | Massachusetts | 87.5% | 1,432 | 202 | 1,636 |
| 34 | Utah | 86.7% | 982 | 151 | 1,133 |
| 35 | California | 85.1% | 6,361 | 1,115 | 7,479 |
| 36 | Alaska | 83.6% | 1,105 | 217 | 1,322 |
| 37 | Wyoming | 83.4% | 646 | 129 | 775 |
| 38 | Illinois | 81.7% | 3,164 | 708 | 3,872 |
| 39 | Tennessee | 80.3% | 1,111 | 272 | 1,383 |
| 40 | Texas | 78.5% | 5,555 | 1,520 | 7,078 |
| 41 | South Dakota | 76.3% | 533 | 166 | 699 |
| 42 | North Dakota | 74.4% | 300 | 103 | 403 |
| 43 | Colorado | 74.4% | 1,642 | 565 | 2,207 |
| 44 | South Carolina | 69.8% | 971 | 421 | 1,392 |
| 45 | Kansas | 66.1% | 688 | 353 | 1,041 |
| 46 | West Virginia | 64.7% | 512 | 279 | 791 |
| 47 | Arkansas | 63.4% | 541 | 312 | 853 |
| 48 | Oklahoma | 62.2% | 780 | 474 | 1,254 |
| 49 | Alabama | 60.1% | 346 | 230 | 576 |
| 50 | District of Columbia | 50% | 6 | 6 | 12 |
| 51 | Kentucky | 30.9% | 135 | 302 | 437 |
Why does groundwater dominate the count?
These shares count systems, not people. The most numerous type, transient non-community systems at places such as gas stations and campgrounds, are 76,476 systems, and 98% of them use groundwater. Community water systems, which include city utilities, use surface water more often: 23% of them draw mainly on surface water, against 9.6% of all systems.
Which states buy the most water from other systems?
A system that buys its water from another public water system is listed with a purchased source. North Dakota has the highest share of systems on purchased water (51%), followed by Kentucky (43%) and District of Columbia (42%). Nationally, 8.8% of active systems buy their water, rising to 20% among community water systems.
Groundwater vs. surface water: frequently asked questions
Do most U.S. public water systems use groundwater or surface water?
Groundwater. 90% of the 142,891 active public water systems in EPA's SDWIS records draw mainly on groundwater, including purchased groundwater.
Which state relies most on groundwater?
Wisconsin: 99% of its 11,056 active systems draw mainly on groundwater. Mississippi (99%) and Minnesota (98%) follow.
Which state relies most on surface water?
Kentucky, where 69% of active systems draw mainly on surface water, followed by District of Columbia (50%).
What does groundwater under the influence of surface water mean?
It is well or spring water that the regulator has found to be affected by nearby surface water, so it is regulated under the surface-water treatment rules. This page counts it with groundwater.
More rankings
About this data
Source: U.S. EPA Safe Drinking Water Information System (SDWIS) and SDWA violation records, via EPA ECHO, as published October 1, 2026 — AquaCensus refreshes it quarterly. See the methodology for how records are matched, cleaned and scored.
Cite as: AquaCensus, “Groundwater vs. surface water, state by state”, https://aquacensus.com/rankings/groundwater-vs-surface-water (data as of October 1, 2026).