Short definition
Annual well water testing is the WA Department of Health-recommended routine for every private well: a yearly mail-in test for total coliform and nitrates, plus a comprehensive heavy-metals panel every 3–5 years. Mortgage closings on private-well properties typically require fresh test results from a state-certified lab.
What it is
WA DOH recommends two layers of well-water testing for homeowners on private wells:
Annual — total coliform plus nitrate. Coliform tells you whether contamination is finding its way into the supply (cracked well cap, surface intrusion, septic too close). Nitrate tracks fertilizer or septic-derived contamination. Both are tasteless and odorless, and both can change without you noticing.
Periodic (every 3–5 years) — a full panel covering arsenic, lead, copper, iron, manganese, hardness, pH, sulfate, fluoride. These don’t change quickly, so a less-frequent comprehensive test makes sense. Areas with documented arsenic (eastern WA agricultural counties) should test arsenic annually.
The test itself is mail-in: you collect a sample per kit instructions, ship it to a state-certified lab, and get results back in 2–4 weeks. The standard panels are inexpensive enough that there’s no good reason to skip them.
Why it matters to a homeowner
Three reasons routine testing is non-negotiable for a private well:
Closings depend on it. Lenders — especially FHA, VA, and USDA — require a fresh coliform (and sometimes nitrate, arsenic) test at closing on private-well properties. A last-minute test that fails delays the closing. Homeowners who test annually have current results in hand and avoid the scramble.
Vulnerable people in the household. Infants under 6 months, immunocompromised individuals, and elderly residents all face higher consequences from contamination. Annual testing catches problems before someone gets sick.
The pathway you can’t see. A cracked well cap, a septic field that’s settling closer to the well, an aquifer level dropping during a dry summer — all of these change the contamination risk without changing how the water tastes. Testing makes the invisible visible.
When you’ll encounter this term
- Annual fall maintenance: schedule the mail-in test
- Pre-listing: order the test 2–4 weeks before listing so results are in hand and any treatment can be deployed
- Post-flooding event: shock chlorinate, then test
- Buying rural property: include a water-test contingency in the offer; require seller to provide results from a state-certified lab
- New baby in the home: fresh comprehensive test before mixing infant formula
Standard cadence and panel
| Test | Cadence | Cost |
|---|---|---|
| Single-parameter coliform | Annual | $25–$60 |
| Coliform + nitrate combined | Annual | $40–$80 |
| Comprehensive heavy-metals panel | Every 3–5 years | $150–$400 |
| Full standard panel (bacteriology + inorganic + metals) | At well install or first occupancy | $250–$500 |
| Radon-in-water (radon-zone counties) | At purchase, then every 5 years | $30–$80 |
Common failure modes (homeowner mistakes)
- Sample contaminated by tap or sample-bottle handling — false-positive coliform; lab requires repeat.
- Wrong sample tap — using an outdoor hose-bib (subject to atmospheric contamination) instead of an indoor cold tap.
- Incomplete flushing before sample — homeowner draws from stagnant line; result not representative.
- Skipping for years, then surprised at sale — last-minute test fails, closing delayed.
- Selecting an uncertified lab — results not accepted by lender or DOH.
How to take the sample correctly
- Use the kit’s sample bottle without rinsing it. The bottle has a preservative.
- Choose an indoor cold tap that gets regular use — kitchen sink is standard.
- Don’t use an outdoor hose bib, a swing-spout filter spout, or any tap with an aerator that’s hard to remove.
- Flush the cold side of the tap for 2–3 minutes before sampling to draw fresh water from the well.
- Don’t touch the inside of the bottle or cap. Don’t let the bottle contact the spout.
- Cap immediately and ship per kit directions, typically same-day or next-day delivery to the lab.
Common variants and disambiguation
- Annual well test (private) vs. utility quarterly/monthly testing (public). Different rules, different scope. Public Group A systems test under WAC 246-290 schedules; private wells follow recommendation, not regulation.
- Real-estate transaction test — minimal panel, often just coliform + nitrate.
- Comprehensive baseline — done at well install or first occupancy; covers parameters that don’t change quickly (As, Pb, fluoride, hardness).
Washington note
WA DOH recommends — but does not regulate — annual coliform + nitrate testing for private single-family wells. Group B systems (2–14 connections, seasonal) follow WAC 246-291 with mandatory periodic monitoring; Group A (15+ connections) follow WAC 246-290.
For real-estate transactions: lenders typically require fresh coliform at closing on private-well properties. FHA, VA, and USDA loans have specific requirements that may go further (nitrate, arsenic, sometimes lead). The seller should provide test results from a state-certified lab.
To find a state-certified lab: check the WA DOH “Drinking Water Laboratories” list. Common WA-region labs include Pace Analytical, Edge Analytical, Tacoma Tap Lab, and Aqua Pure. Some utilities (Tacoma Water, Seattle Public Utilities) offer no-charge coliform testing for customers with concerns — different from a private-well test, but useful if you’re trying to compare results.