Who looks after a shared well?
Group B water systems are small public systems: in Thurston County, a well serving 3 to 14 connections and fewer than 25 people a day. The county's Environmental Health Division regulates all of them. The owner, or the agency running the system, must test for coliform yearly and nitrate every 36 months, and warn users within 24 hours of an E. coli or high-nitrate result.
Street to Drainfield · updated · sources listed at the end
How does Thurston County classify a shared well?
By the number of homes it serves. The county's Drinking Water and Wells page sets out four classes, as read on 6 November 2026:
- Non-public well: one single-family connection, or an irrigation well.
- Two single-family residential water supply: one well serving two homes.
- Group B public water system: 3 to 14 connections and fewer than 25 people a day, or 25 or more people a day on fewer than 60 days a year.
- Group A public water system: 15 or more connections, or 25 or more people a day for 60 days or more a year.
DOH describes Group B the same way at state level: fewer than 15 connections and fewer than 25 people a day.
Who regulates Group B water systems here?
Thurston County Environmental Health. DOH's Group B page explains that the state rule, chapter 246-291 WAC, took effect on January 1, 2014, and lets local health jurisdictions adopt stricter rules. Thurston County's systems must meet Article III of the county Sanitary Code as well as the state rule. New systems must be owned or professionally managed by an approved Satellite Management Agency, one of the agencies on DOH's approved list, which DOH says may help with sampling, repair, maintenance and inspection.
What sampling must a Group B system do?
The county page lists the schedule:
- Coliform bacteria: at least once every 12 months, from the far end of the distribution system or where the county directs.
- Nitrate: every 36 months, starting 36 months after a new system's first inorganic analysis.
- Other contaminants: where contamination is known, or where the system treats water, with samples before and after treatment.
All samples go to a state-certified lab, and the lab form must carry the system name, ID number and "Group B", or the system gets no credit. DOH recommends coliform and nitrate at least yearly for any Group B system, so a yearly nitrate test goes beyond the county minimum.
What must the operator tell users after a bad result?
Within 24 hours, the system's purveyor must notify the county, the health officer and every user if a certified lab finds E. coli, finds nitrate at or above 10.0 mg/L, or a threat of acute contamination such as a flood arises. DOH also has template notices for these cases. Power outages and pump failures must be passed on to users too. What those results mean for your household is covered on the coliform and nitrate pages.
What about one well shared by two homes?
It is a separate class with lighter rules. Thurston County regulates two-home wells and recommends a coliform test every year and nitrate every 3 years, a written Shared Well Agreement between the two parties, and an access agreement filed with the County Auditor when the two parcels are separate legal lots. Adding a third connection turns the well into a Group B system, which needs a professional engineer's design and county approval.
What should you do if you get water from a Group B system?
Stay in touch with whoever runs it. DOH advises Group B users to talk regularly with the system's owner and operator, and notes the operator must tell you about contamination. Ask for the latest coliform and nitrate reports. If you do not know who runs your system, the county's Water Lab page points to DOH's public water system database. For the parts of the pipe that are yours, see who owns which pipe.
Yours to do
- Ask the system's operator for the most recent coliform and nitrate results.
- Keep the 100-foot area around the well clear of anything the covenant bars.
- Pass on any change in taste, color or pressure to the operator quickly.
- Read your Shared Well Agreement if you are on a two-home well.
Leave to a licensed or certified pro
- Sampling and system repairs by the operator or a Satellite Management Agency.
- New systems and expansions designed by a licensed professional engineer and approved by the county.
- Well, pump and tank work by a licensed well driller or pump installer; wiring by a licensed electrician.
On the record
- 3–14Connections that make a Group B system in Thurston CountyThurston County Environmental Health
- 12 monthsMaximum gap between Group B coliform samplesThurston County Environmental Health
- 36 monthsGroup B nitrate sampling intervalThurston County Environmental Health
- 24 hoursDeadline to notify users of E. coli or high nitrateThurston County Environmental Health
- 100 feetUsual radius of the protected area around the wellThurston County Environmental Health
| Water supply type | Connections | Who regulates |
|---|---|---|
| Non-public well | 1 home | Thurston County Environmental Health (siting, approval) |
| Two single-family supply | 2 homes | Thurston County Environmental Health |
| Group B public system | 3 to 14 | Thurston County Environmental Health, under WAC 246-291 |
| Group A public system | 15 or more | Washington DOH |
Common questions
Does a Group B system need a water right?
The county page says a permit from Ecology is needed if system-wide use exceeds 5,000 gallons a day, or if irrigation served by the system exceeds half an acre.
Can a Group B system add more homes?
Only with county approval of plans first. If it will eventually serve more than 14 homes, the county says to proceed as a Group A system.
What arsenic limit applies to a Group B system?
DOH says the 10 parts per billion standard applies to new or expanding systems approved after January 1, 2014. Older systems may exceed it without being out of compliance, so ask for results.
What happens if a Group B system ignores the rules?
The county says enforcement can include notifying customers, lenders or building authorities, which can affect loans and building permits.
Sources
- Drinking Water and Wells, Thurston County Environmental Health — classes, sampling schedule, notification, covenants, two-home wells, water rights; read 6 November 2026
- Group B Water Systems, Washington DOH — definition, WAC 246-291, local rules, accredited labs; read 6 November 2026
- Group B Information for Consumers, Owners, and Operators, Washington DOH — user contact with operator, arsenic standard; read 6 November 2026
- Operating Your Group B System, Washington DOH — yearly sampling advice, Satellite Management Agencies; read 6 November 2026
- Water Lab, Thurston County Environmental Health — finding who runs a public system; read 6 November 2026
- Chapter 246-291 WAC, Group B Public Water Systems — state rule text; read 6 November 2026
How this page was put together. This page is built on Thurston County Environmental Health's drinking water page and Washington DOH's Group B pages, read on 6 November 2026, with the state rule linked for detail. It summarizes duties as those agencies publish them and does not interpret the Sanitary Code for any particular system. For a ruling on your system, ask the county.
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