Typical values from 375 sampled wells in Riverside County · Full groundwater profile
What Are You Noticing in Your Water?
Pre-selected from Riverside County well data. Untick anything you do not notice in your own water.
Based on the contaminants most commonly reported in this region. Always confirm with a certified lab water test before buying equipment.
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Riverside County has about 2,492,000 residents, and its largest communities are Riverside, Moreno Valley and Corona. Homes outside city and community water systems rely on private domestic wells. Wells here tap the Basin and Range basin-fill aquifers, and the largest DWR groundwater basin in the county is Chuckwalla Valley.
Across 374 sampled wells, groundwater is very hard (10.6 gpg in the typical well). Arsenic exceeded the 10 µg/L drinking water limit in 10% of 347 sampled wells; nitrate exceeded the 10 mg/L drinking water limit in 21% of 358 sampled wells; hexavalent chromium (chromium-6) exceeded the 10 µg/L drinking water limit in 11% of 172 sampled wells. These have no taste or smell, so only a lab test shows whether your own well is affected.
In this guide
Groundwater Profile: Riverside County
Most groundwater pumped in Riverside County comes from the Basin and Range basin-fill aquifers (USGS Principal Aquifers map). Across 374 sampled wells, the median hardness is 10.6 gpg, which the USGS classes as very hard. The largest California DWR Bulletin 118 groundwater basins in the county are Chuckwalla Valley, Coachella Valley – Indio and Palo Verde Mesa.
What shows up in local well samples:
- HardnessMedian 10.6 gpg; 73% of 374 sampled wells above 7 gpg
Calcium and magnesium dissolved from limestone. Leaves scale on fixtures and water heaters and reduces soap lather. Not a health risk. Planning a salt-based softener? California Water Code Section 13148 lets some local sewer and water recycling agencies limit or ban new salt-discharging softeners, so check with yours first. Salt-free conditioners discharge no brine but do not soften water; see what salt-free systems can and cannot do.
Water softener sizing - Nitrate21% of 358 sampled wells above 10 mg/L
A health risk for infants above the EPA limit of 10 mg/L, usually from fertilizer, septic systems or livestock. Only a lab test detects it.
How to test your well - Arsenic10% of 347 sampled wells above 10 µg/L
Odorless and tasteless, with an EPA limit of 10 µg/L. Only a lab test detects it.
How to test your well - Chromium-611% of 172 sampled wells above 10 µg/L
Hexavalent chromium, odorless and tasteless, from natural geology and some industrial sites. California’s drinking water limit has been 10 µg/L since October 1, 2024. Only a lab test detects it.
How to test your well
Hydrogen sulfide was above 0.1 mg/L in 12% of 34 wells tested in Riverside County, so a rotten-egg smell is possible but not typical.
Arsenic, Nitrate, Chromium-6 and Salinity in Riverside County
| Contaminant | Typical well | Wells above limit | California standard |
|---|---|---|---|
| Arsenic | 1 µg/L | 10% of 347 | 10 µg/L (primary MCL) |
| Nitrate (as nitrogen) | 2.03 mg/L | 21% of 358 | 10 mg/L (primary MCL) |
| Chromium-6 | 2 µg/L | 11% of 172 | 10 µg/L (primary MCL since Oct. 1, 2024) |
| Salinity (dissolved solids) | 414 mg/L | 10% of 375 | 500 mg/L recommended, 1,000 mg/L upper (secondary) |
| Hardness | 10.6 gpg | 73% of 374 | No limit; above 7 gpg is hard |
Typical well = median of sampled wells; salinity column counts wells above 1,000 mg/L and hardness wells above 7 gpg. Standards: California State Water Resources Control Board (Title 22 maximum contaminant levels). Samples: USGS and EPA Water Quality Portal, wells sampled since 2000.
How Riverside County Compares to California and the U.S.
See How Riverside County Compares to California & the US
| Share of wells with… | Riverside CountyRiverside | CaliforniaCA | United StatesUS |
|---|---|---|---|
| Hard water (above 7 gpg) | 73% | 64% | 60% |
| Iron above 0.3 mg/L | 2% | 9% | 19% |
| Manganese above 0.05 mg/L | 9% | 22% | 21% |
| Dissolved solids above 500 mg/L | 40% | 38% | 15% |
| Acidic water (pH below 6.5) | 0% | 2% | 14% |
| Nitrate above 10 mg/L (EPA limit) | 21% | 9% | 4% |
| Arsenic above 10 µg/L (EPA limit) | 10% | 14% | 7% |
| Chromium-6 above 10 µg/L (California limit) | 11% | 6% | — |
| Median hardness | 10.6 gpg | 9.9 gpg | — |
| Median pH | 7.8 | 7.6 | 7.3 |
Riverside County and California: share of sampled wells (all well types, samples since 2000) whose typical value exceeds the level, from the Water Quality Portal. United States: USGS Circular 1332, about 2,100 domestic wells in 48 states sampled 1991 to 2004. Well types and years differ, so read this as a broad comparison. Highlighted cells are well above the national share.
See what a typical Riverside County well needs
Opens the diagnostic calculator with Riverside County median values (10.6 gpg hardness, 0 ppm iron, pH 7.8) for a 3–4 person home. Swap in your own lab results for an exact plan.
Testing Your Well in Riverside 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 Riverside 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
- Arsenic, which appeared above the 10 µg/L limit in some sampled wells here
- Hexavalent chromium (chromium-6), which appeared above California’s 10 µg/L limit in some sampled wells here
- After any flood, new well work or a change in taste, color or smell
Statewide guidance is on the State Water Board domestic well testing page, and our guide to how to test well water covers which tests to order.
Nearby Counties
Riverside County borders these counties with published reports:
Frequently Asked Questions
How hard is well water in Riverside County?
Groundwater samples from 374 wells in Riverside County have a median hardness of 10.6 grains per gallon (181 mg/L), which the USGS classes as very hard. About 73% of sampled wells are above 7 gpg, the point where a water softener is usually worthwhile. The California statewide median is 9.9 gpg.
Is iron a problem in Riverside County well water?
The median iron level across 375 sampled wells is 0 mg/L, below the EPA aesthetic guideline of 0.3 mg/L, and 2% of wells exceed it. 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 Riverside County?
Hydrogen sulfide was above 0.1 mg/L in 12% of 34 wells tested in Riverside County, so a rotten-egg smell is possible but not typical. The smell is a nuisance rather than a health risk at typical levels.
Which aquifer supplies wells in Riverside County?
Most groundwater pumped in Riverside County comes from the Basin and Range basin-fill aquifers (USGS Principal Aquifers map).
Is chromium-6 a concern in Riverside County well water?
Hexavalent chromium was above California’s 10 µg/L drinking water limit in 11% of 172 sampled wells in Riverside County. The limit took effect on October 1, 2024. It has no taste or smell, so only a lab test shows whether your well is affected; reverse osmosis is a common household treatment.
Can I install a salt-based water softener in Riverside 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 Riverside County?
Only if bacteria are the problem. A one-minute rolling boil kills germs, but it does not remove nitrate, arsenic or other chemicals, and it concentrates them as water evaporates. Test first, and see our boiling well water myth buster for when boiling helps.
How often should I test my well water in Riverside 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.