Town by Town: Who Supplies the Water, and From Where

Six communities share this corner of north San Luis Obispo County, and no two get their water the same way. The towns run public systems with their own wells, and some add lake water piped from Nacimiento. Outside those lines, the household well is the water company. Below, each town's supplier, its sources, its hardness where a recent report publishes it, and the septic and groundwater agencies that matter there. We could not retrieve current hardness figures for Paso Robles or Templeton, so the annual water quality report each supplier mails or posts is the place to look.

Paso Robles

The city's water page says that in a normal year more than half its water comes from seven fairly shallow wells along the Salinas River, supplemented by Nacimiento Water Project surface water and wells in the basin. The city holds a Nacimiento entitlement of 6,488 acre-feet a year and used 1,909 acre-feet of it in water year 2025. The basin's annual report notes that its river wells draw underflow regulated as surface water, from the Thunderbird Wells in the neighboring Atascadero Subbasin.

The city is its own groundwater agency inside the Paso Robles Area Groundwater Authority. The county septic program does not cover land inside city limits, though two county nitrogen focus areas sit at its edges: Jardine Road, described as the northeast part of the city, and Branch Road, two miles east. Our hard water numbers brief collects the published figures.

Templeton

The Templeton Community Services District describes twelve active wells, four of them on standby, and four storage tanks holding 2.7 million gallons, serving 3,000 connections and about 8,011 people. That description comes from an archived copy of the district's page; its 2025 water quality report was not available to us. Templeton North, three miles south of Paso Robles, is a moderate-impact area where new homes on septic need a nitrogen-reducing system, covered in nitrogen-reducing septic areas.

Atascadero

Atascadero Mutual Water Company pumps from 15 wells drawing on the Atascadero Basin and Salinas River underflow, and also takes Lake Nacimiento water through the Nacimiento pipeline. Its 2025 water quality report gives total hardness as 20.2 grains per gallon on average, ranging from 16 to 26. The USGS calls water above 180 mg/L very hard; at 17.1 mg/L to the grain, Atascadero's average lands far past that mark. The City of Atascadero has its own septic management program, approved on December 7, 2018, separate from the county's.

San Miguel

The San Miguel Community Services District runs on groundwater wells alone. Its 2025 report gives hardness at 317 ppm on average, ranging from 263 to 358, along with an average of 4.8 ppm nitrate as nitrogen in raw well water, 4.0 ppb arsenic and 14.6 pCi/L gross alpha, against limits of 10 ppm, 10 ppb and 15 pCi/L. The report rates its wells most vulnerable to nearby septic and sewer systems, though no detected contaminant is tied to them. The district's groundwater agency did not join the basin authority in 2025.

Creston

Creston has no town water system in the sources we read; homes rely on private wells in the Paso Robles subbasin. The Estrella-El Pomar-Creston Water District, formed in 2017, became a groundwater agency on June 6, 2023, and is a member of the basin authority. Creston is listed as a severe-impact septic area, so new construction there needs a nitrogen-reducing system under the county program approved in 2020.

Shandon

Shandon sits about 12 miles east of Paso Robles and is a moderate-impact septic area for new construction. The Shandon-San Juan Water District is one of the four members of the basin authority. State Water Project water can reach Shandon, the basin's annual report says, but homes outside any water system rely on their own wells.

Outside town water lines

For most ranchettes, vineyard homes and oak-woodland parcels, the supplier is the well in the yard. No agency checks that water for you: the county's well owner page puts the safety of a private well squarely on its owner. Start with living on a private well and testing your well water. A parcel with both its own well and septic system needs at least 2.5 acres under the county septic program. Homes that run short can buy hauled water, which the state health department licenses for loads of 250 gallons or more; see hauled water for rural homes. Basin rules for household pumpers are in household wells and the basin rules.

Where to call

• City of Paso Robles — city water sources and the annual water quality report. About Our Water
• Templeton Community Services District — district water service and reports. Water page
• Atascadero Mutual Water Company — water quality reports and hardness. Water quality
• San Miguel Community Services District — water service, reports and its groundwater agency. District site
• Estrella-El Pomar-Creston Water District — groundwater agency for its area around Creston. District site
• Paso Robles Area Groundwater Authority — which member agency covers a rural parcel. Member agencies

Sources

1. City of Paso Robles — About Our Water (archived copy, October 2026) — city sources and Nacimiento entitlement
2. Paso Robles Subbasin Water Year 2025 Annual Report — Thunderbird Wells, 2025 Nacimiento use, Shandon State Water Project, Creston district as an agency
3. Templeton Community Services District — Water (archived copy) — wells, tanks, connections and population
4. Atascadero Mutual Water Company — Water quality reports — sources and 2025 hardness
5. San Miguel Community Services District — 2025 Consumer Confidence Report — sources, hardness, nitrate, arsenic, gross alpha
6. Central Coast Water Board — staff report on the county septic program, September 2020 — nitrogen focus areas, city exclusions
7. Central Coast Water Board — local septic management programs — Atascadero program approved December 7, 2018
8. Paso Robles Area Groundwater Authority — Member Agencies — authority members
9. USGS — Hardness of Water — hardness scale
10. County of San Luis Obispo — Local Agency Management Program (archived copy, July 2026) — 2.5-acre minimum with well and septic
11. California Department of Public Health — Food and Drug Branch, water haulers — hauler licensing for 250 gallons or more
12. County of San Luis Obispo — Private Well Owner Resources — owner responsible for private well water