Douglas County, Colorado has about 393,995 residents (Census 2024 estimate) and 29 community water systems in EPA records. The largest local system is Castle Rock Town of, serving about 110,298 people from surface water.
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
Castle Rock Town of Estimate: untreated local water, not your tap · Low confidence
7.0 gpg (120 mg/L), moderately hard
Douglas County: median of 1,785 results from 337 monitoring sites (streams and wells). Utilities may blend or treat water, so your tap can differ.
Source: Hard Water Map county data, samples through 2025
County estimates: Hard Water Map (hardwatermap.com), CC BY 4.0, derived from the USGS/EPA Water Quality Portal; file generated 2026-07-22. License
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
For a 3-person home using 57 gallons per person per day and regenerating weekly, you'd remove about 8,379 grains between regenerations. Suggested size: 24,000 grain. This uses a low-confidence county estimate, so confirm with a test first.
Estimate only. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
The 6 biggest of 29 community water systems on EPA records for this county. Service areas don't follow county lines; your water bill names your provider.
CO0118010 · serves about 110,298 people · Surface water
Lead 90th percentile: 2 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
CO0118015 · serves about 103,444 people · Surface water
Lead 90th percentile: 3 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
CO0118040 · serves about 75,949 people · Surface water
Lead 90th percentile: 2.6 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
CO0218015 · serves about 23,415 people · Surface water
Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
CO0118076 · serves about 15,295 people · Surface water
Lead 90th percentile: 2 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
CO0118055 · serves about 13,765 people · Surface water
Lead 90th percentile: 5 ppb (period starting 2023-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
A PFAS detection is not a violation. Federal limits (4 ppt for PFOA and PFOS) apply to running annual averages, with compliance required by 2029. In May 2026 EPA proposed extending the PFOA/PFOS deadline to 2031 and removing other PFAS limits; not final as of 2026-10-21.
These are public records for whole systems. Your home's pipes, fixtures and any private well can change what you drink. A certified lab test or a hardness test strip gives you your own numbers. Then use our PFAS and lead filter selector to see which certifications to look for.
None of the 6 largest systems here have a health-based violation in EPA records since October 2021. Castle Rock Town of's most recent lead 90th percentile was 2 ppb (2026), below the 15 ppb action level. Public records can't guarantee what comes out of your tap, especially with older plumbing, so a home test is the surest check.
There's no published utility figure in our data, but untreated local stream and well samples in Douglas County have a median of about 7.0 grains per gallon (120 mg/L, moderately hard). That's a low-confidence estimate of source water, not your tap, so test before you buy equipment. For a 3-person home at 7 gpg, our softener calculator suggests a 24,000 grain unit as a starting point.
4 of the 6 sampled systems listed here detected at least one PFAS in EPA's UCMR 5 testing, and 3 results were above the level of a federal limit in at least one sample. A detection isn't a violation: federal PFAS limits apply to running annual averages starting in 2029.
Most homes are served by Castle Rock Town of or one of the other systems listed on this page, but service areas don't follow county lines. Your water bill names your provider, and its annual Consumer Confidence Report has the full test results.
Data as of October 21, 2026. Figures are copied from public records and combined with our own calculations; they can be out of date or wrong. Tapped Out isn't affiliated with any utility or the EPA. Written and reviewed by the Tapped Out team. How we calculate · All sources.