Water Quality Report · Updated October 07, 2026
GSWC - SOUTHWEST
GSWC - SOUTHWEST delivers tap water graded C (73/100) by TapWaterSafety.org. The utility serves approximately 277,740 residents in HAWTHORNE, California using surface water (purchased). The most significant water quality concerns are: Haloacetic acids (HAA5) significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline; Total trihalomethanes (TTHMs) significantly above health guideline; Arsenic detected. For questions, the utility can be reached at 310-263-4141.
Is HAWTHORNE tap water safe to drink?
GSWC - SOUTHWEST delivers tap water that earns a grade of C (73/100) from TapWaterSafety.org — an average rating, with several contaminants above health guidelines but generally compliant with US legal limits.
The utility serves 277,740 residents in HAWTHORNE, drawing from surface water (purchased).
Public testing data identifies 15 contaminants in this water above EWG's health-based guidelines, including: Haloacetic acids (HAA5), Haloacetic acids (HAA9), Total trihalomethanes (TTHMs), Bromodichloromethane, Arsenic, Dibromochloromethane, Dibromoacetic acid, Chloroform, Trichloroacetic acid, Dichloroacetic acid, Bromoform, Nitrate*, Nitrate and nitrite*, Radium, combined (-226 and -228)*, Chromium (hexavalent). For most residents, a properly certified home filter at the kitchen tap is the most cost-effective way to reduce exposure to whatever's in your water. See our filter recommendations below, matched specifically to this utility's contaminant profile.
EPA compliance record
Official U.S. EPA records for GSWC - SOUTHWEST (system ID CA1910155) for the last 3 years. Checked 2026-10-07.
Source: U.S. EPA Enforcement and Compliance History Online (ECHO), from the Safe Drinking Water Information System. See EPA's full report.
Quick actions for HAWTHORNE residents
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for GSWC - SOUTHWEST.
Haloacetic acids (HAA5) significantly above health guideline
Moderate concernHaloacetic acids (HAA5) detected at 36.2 ppb, 362x above the EWG health guideline of 0.1 ppb.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 15.1 ppb, 252x above the EWG health guideline of 0.06 ppb.
Total trihalomethanes (TTHMs) significantly above health guideline
Moderate concernTotal trihalomethanes (TTHMs) detected at 28.0 ppb, 186x above the EWG health guideline of 0.15 ppb.
Arsenic detected
Moderate concernArsenic detected at 0.446 ppb.
Contact GSWC - SOUTHWEST
Reach the utility directly for service issues, water quality concerns, or to request your Consumer Confidence Report.
General Contact
Treatment Plant
Recommended water filters for HAWTHORNE
Filters matched to the specific contaminants in this water supply.
Carbon filter certified for VOCs (NSF/ANSI 53)
$180-$599Activated carbon is effective for disinfection byproducts. Look for NSF/ANSI 53 VOC reduction.
Reverse osmosis certified for arsenic (NSF/ANSI 58)
$429-$599Reverse osmosis certified under NSF/ANSI 58 for arsenic is the most reliable home option.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
Score breakdown
This utility's overall score of 73/100 breaks down across five weighted components. Read the full methodology →
Contaminants detected — international standards comparison
Every contaminant detected, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal (the strictest US benchmark). Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Haloacetic acids (HAA5) Disinfection byproduct |
36.2 ppb | 0.1 | 60.0 | 60 | — | — | — | 362× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
15.1 ppb | 0.06 | — | — | — | — | — | 252× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
28.0 ppb | 0.15 | 80.0 | 100 | — | — | — | 186× over |
| Bromodichloromethane Disinfection byproduct |
7.33 ppb | 0.06 | — | — | — | — | — | 122× over |
| Arsenic Heavy metal |
0.446 ppb | 0.004 | 10.0 | 10 | 10 | 0.004 | — | 112× over |
| Dibromochloromethane Disinfection byproduct |
8.98 ppb | 0.1 | — | — | — | — | — | 90× over |
| Dibromoacetic acid Disinfection byproduct |
1.76 ppb | 0.03 | — | — | — | — | — | 59× over |
| Chloroform Disinfection byproduct |
6.94 ppb | 0.4 | — | — | — | — | — | 17× over |
| Trichloroacetic acid Disinfection byproduct |
1.6 ppb | 0.1 | — | — | — | — | — | 16× over |
| Dichloroacetic acid Disinfection byproduct |
3.06 ppb | 0.2 | — | — | — | — | — | 15× over |
| Bromoform Disinfection byproduct |
4.69 ppb | 0.5 | — | — | — | — | — | 9.4× over |
| Nitrate* Inorganic |
0.281 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 2.0× over |
| Nitrate and nitrite* Inorganic |
0.287 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 2.0× over |
| Radium, combined (-226 and -228)* Radiological |
0.07 pCi/L | 0.05 | 5.0 | — | — | — | — | 1.4× over |
| Chromium (hexavalent) Heavy metal |
0.0209 ppb | 0.02 | — | — | — | — | — | 1.0× over |
| Uranium Radiological |
0.31 pCi/L | 0.43 | 20.0 | 30 | 30 | 0.43 | — | Below guideline |
| Chlorate Disinfection byproduct |
148.4 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Chloromethane Other |
0.978 ppb | 2.69 | — | — | — | — | — | Below guideline |
| Aluminum* Heavy metal |
77.5 ppb | 600.0 | — | 200 | — | 600 | — | Below guideline |
| Molybdenum Other |
3.35 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Vanadium Other |
0.767 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Manganese Heavy metal |
2.9 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Barium Heavy metal |
18.5 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Strontium Radiological |
0.539 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Bromomethane Other |
0.135 ppb | — | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.477 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| Lithium Other |
10.3 ppb | — | — | — | — | — | — | Below guideline |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines (4th ed.), California OEHHA PHGs, EWG Tap Water Database.
GSWC - SOUTHWEST service area
This water system serves 1 community in Los Angeles County, California. Click any city for its dedicated tap water quality page.
Find the right filter for HAWTHORNE water
Browse filter categories by water-quality concern. Each option below is NSF-certified for the matched contaminant type.