Typical values from 13 sampled wells in Yolo County · Full groundwater profile
What Yolo County Wells Usually Need
No common nuisance problem in the typical well. The typical Yolo well is very hard, with iron below the stain threshold and a pH of 7.7.
Drink it untreated? Most sampled wells meet health limits; a yearly test confirms yours does.
Typical treatment, in plumbing order:
Usually nothing beyond routine testing. Most Yolo wells need no softener or iron filter, so test before buying equipment.
Not sure what to install? Get a filter recommendation for Yolo County homesOn city or county water instead? Your utility publishes an annual water quality report; this page covers private wells. Find your utility's report
On this page (8 sections)
Where to Test Well Water in Yolo County
- Your county environmental health department handles private well questions in Yolo County; for a water test, use a state-accredited lab, many of which accept mailed or dropped-off samples.
- Certified labs: State Water Board list of accredited labs (ELAP)
Ask the lab for sample bottles and how quickly the sample must reach it before you collect.
What Are You Noticing in Your Water?
Confirm with a lab test before buying equipment.
Explore California Interactive Map
Explore Yolo County and nearby counties
Yolo County has about 221,000 residents, and its largest communities are Davis, Woodland and West Sacramento. Homes outside city and community water systems rely on private domestic wells. Wells here tap the Central Valley aquifer system, and the largest DWR groundwater basin in the county is Sacramento Valley – Yolo.
Across 13 sampled wells, groundwater is very hard (14.6 gpg in the typical well). Arsenic, nitrate and chromium-6 were below California limits in most sampled wells, but individual wells vary, so test yours.
In this guide
Groundwater Profile: Yolo County
The largest California DWR Bulletin 118 groundwater basin in the county is Sacramento Valley – Yolo.
Another address? Check hardness by ZIP code.
What shows up in local well samples:
- HardnessLimited local data (fewer than 20 samples): individual well testing recommended.
Calcium and magnesium dissolved from limestone. Leaves scale on fixtures and water heaters and reduces soap lather. Not a health risk.
Water softener sizing
Arsenic, Nitrate, Chromium-6 and Salinity in Yolo County
| Contaminant | Typical well | Wells above limit | California standard |
|---|---|---|---|
| Arsenic | 3.7 µg/L | Limited data (13 wells) | 10 µg/L (primary MCL) |
| Nitrate (as nitrogen) | 0.95 mg/L | Limited data (13 wells) | 10 mg/L (primary MCL) |
| Chromium-6 | 2.22 µg/L | Limited data (7 wells) | 10 µg/L (primary MCL since Oct. 1, 2024) |
| Salinity (dissolved solids) | 412 mg/L | Limited data (13 wells) | 500 mg/L recommended, 1,000 mg/L upper (secondary) |
| Hardness | 14.6 gpg | Limited data (13 wells) | No limit; above 7 gpg is hard |
Typical well = median. Standards: State Water Board; samples: Water Quality Portal, since 2000.
How Yolo County Compares to California and the U.S.
See How Yolo County Compares to California & the US
| Share of wells with… | Yolo CountyYolo | CaliforniaCA | United StatesUS |
|---|---|---|---|
| Hard water (above 7 gpg) | Limited data | 64% | 60% |
| Iron above 0.3 mg/L | Limited data | 9% | 19% |
| Manganese above 0.05 mg/L | Limited data | 22% | 21% |
| Dissolved solids above 500 mg/L | 31% | 38% | 15% |
| Acidic water (pH below 6.5) | 0% | 2% | 14% |
| Nitrate above 10 mg/L (EPA limit) | Limited data | 9% | 4% |
| Arsenic above 10 µg/L (EPA limit) | Limited data | 14% | 7% |
| Chromium-6 above 10 µg/L (California limit) | Limited data | 6% | — |
| Median hardness | 14.6 gpg | 9.9 gpg | — |
| Median pH | 7.7 | 7.6 | 7.3 |
Sources: Water Quality Portal (since 2000); US: USGS Circular 1332. Highlighted: well above the US share.
See what a typical Yolo County well needs
Pre-filled with the Yolo medians. Swap in your own results.
Testing Your Well in Yolo County
In California, county environmental health departments handle private well permits and can advise on testing. For bacteria, nitrate, arsenic or a full panel, use a laboratory accredited by California’s Environmental Laboratory Accreditation Program (ELAP); the State Water Board’s certified lab map lists them.
What to test for in Yolo County:
- Bacteria (total coliform and E. coli), nitrate and arsenic, at least once a year (California State Water Resources Control Board recommendation)
- Hardness in grains per gallon (gpg) to size a softener
- After any flood, new well work or a change in taste, color or smell
Which tests to order and how: how to test well water.
After a positive coliform test, shock the well with the right bleach dose and retest 10 to 14 days later.
Nearby Counties
Yolo County borders these counties with published reports:
Colusa County
17.4 gpg hardness · Hardness, ManganeseLake County
9.1 gpg hardness · HardnessNapa County
5.2 gpg hardness · Manganese, ArsenicSacramento County
6.8 gpg hardness · Arsenic, Chromium-6Solano County
13.9 gpg hardness · Hardness, Total dissolved solidsSutter County
15.2 gpg hardness · Hardness, ArsenicCounties with similar well water
Elsewhere in California, these counties have well water like Yolo County:
Frequently Asked Questions
Is well water in Yolo County safe to drink?
Most Yolo wells meet health limits in lab records (13 wells sampled). A yearly bacteria and nitrate test is what tells you about your own well.
How hard is well water in Yolo County?
Groundwater samples from 13 wells in Yolo County have a median hardness of 14.6 grains per gallon (250 mg/L), which the USGS classes as very hard. Limited local data (fewer than 20 samples): individual well testing recommended. The California statewide median is 9.9 gpg.
Is iron a problem in Yolo County well water?
The median iron level across 13 sampled wells is 0 mg/L, below the EPA aesthetic guideline of 0.3 mg/L (limited local data (fewer than 20 samples): individual well testing recommended). Most wells will not stain, but if yours does, a lab test tells you whether iron or manganese is the cause.
Why does my well water smell like rotten eggs in Yolo County?
The data cannot say: just 4 Yolo wells were tested for hydrogen sulfide. If your water smells, test for sulfide, and if the smell is only in hot water, check the water heater anode rod. It is unpleasant but rarely a health risk.
Is chromium-6 a concern in Yolo County well water?
Only 7 wells in Yolo County have been sampled for hexavalent chromium, too few to say how common it is. California’s limit is 10 µg/L, and only a lab test of your own well can show whether it is affected.
Can I install a salt-based water softener in Yolo County?
Usually, but check local rules first. California Water Code Section 13148 lets some local sewer and water recycling agencies limit or ban new salt-discharging softeners to protect recycled water. Homes on septic systems should ask the county environmental health department about brine. A salt-free conditioner discharges no brine, but it reduces scale rather than softening the water.
Does boiling well water make it safe to drink in Yolo County?
For a bacteria problem, yes: boil for one minute (three above 6,500 feet). For anything chemical, no, because evaporation concentrates it. Our boiling well water myth buster explains the difference.
How often should I test my well water in Yolo County?
The California State Water Resources Control Board recommends testing domestic wells every year, including for bacteria, nitrate and arsenic, and again after flooding or well repairs.
Written by Well Water Advisor Editorial Team.