Silver Spring Tap Water by the Numbers (2026)

Silver Spring tap water at a glance:

• 1.9 million people served by WSSC Water, through 438,639 service connections
• Haloacetic acids (HAA5): 49 ppb, 490× EWG's health guideline
• Trihalomethanes (TTHMs): 66 ppb, 440× EWG's guideline
• Chromium-6: 0.13 ppb, 6× EWG's guideline
• Arsenic: detected, 10× EWG's guideline
• Lead, 90th percentile: 1.05 ppb, 5.3× EWG's guideline of 0.2 ppb
• PFAS: 2 compounds found, both under EWG's standard
• Federal limits: every one that applies is met, with no violations on file

That last line matters most for the legal question. Silver Spring's water is fully legal to drink. The rest of the list shows how it compares with the Environmental Working Group's (EWG) stricter, health-only guidelines. Here is what each number means, in a few minutes of reading.

1.9 million people, 438,639 connections

Silver Spring does not treat its own water. It is served by WSSC Water, the Washington Suburban Sanitary Commission, which serves about 1.9 million people across both Montgomery County and Prince George's County. On the EPA's record, that supply runs through 438,639 service connections.

WSSC Water draws surface water from the Potomac River and the Patuxent River. Treatment includes powdered activated carbon, algae control, coagulation, flocculation, rapid sand filtration and fluoridation, followed by disinfection.

Scale is the key to the rest of this article. A system this size runs a long distribution network, and water can spend days in the pipes between the plant and a Silver Spring kitchen. Our report covers ZIP codes 20901, 20902, 20903, 20904, 20906 and 20910, plus surrounding Silver Spring areas.

490× and 440×: the disinfection byproducts

The two largest numbers belong to the same family. Haloacetic acids average 49 ppb against an EWG guideline of 0.1 ppb. Total trihalomethanes average 66 ppb against a guideline of 0.15 ppb.

Neither one comes from the river. Surface water needs heavy disinfection, and when chlorine reacts with natural organic matter in the water, these byproducts form. They form in the pipes after treatment rather than at the plant, so those days in a long network give them time to build.

EWG links haloacetic acids to cancer. It links trihalomethanes to cancer and to effects on fetal development.

6× and 10×: chromium-6 and arsenic

Contaminant	Found	EWG guideline	Over by
Chromium-6	0.13 ppb	0.02 ppb	6×
Arsenic	Detected	0.004 ppb	10×

Source: WSSC Water data via EWG.

These multiples are much smaller than the byproduct figures, but they are still above EWG's guidelines. EWG links chromium-6, also called hexavalent chromium, to stomach cancer. It links arsenic to cancer, cardiovascular effects and developmental effects.

One note on reading the "Over by" column: it compares each level with EWG's health guideline, not with the federal legal limit.

1.05 ppb: the lead number

Lead is measured differently. Utilities sample taps inside homes and report the 90th percentile. For WSSC Water, that was 1.05 ppb, which means nine in ten homes tested came in below it and one in ten came in above it.

Two comparisons put it in context:

• Against the EPA: well under the action level, which is being lowered from 15 ppb to 10 ppb, in force November 2027.
• Against EWG: about 5.3 times EWG's guideline of 0.2 ppb. EWG links lead to harm to the brain and nervous system.

Lead mostly comes from service lines and household plumbing, so your home's result can be higher or lower than the utility figure.

2 PFAS compounds, both under EWG's standard

In the EPA's latest national monitoring round (UCMR5, 2023 to 2025), 2 PFAS compounds turned up in this supply: PFPeA at 6.7 ppt and PFHxA at 4.8 ppt. Note the unit. These are parts per trillion, a thousand times smaller than the parts per billion used above.

Both came in under EWG's health standard, and no federal limit exists for either. EWG links them to harm to fetal growth and child development. Standard treatment is not designed to remove PFAS, which is why the monitoring result is worth knowing.

Legal, and still over a guideline

How can water be fully legal and 490 times over something? The two numbers use different yardsticks.

Federal limits are enforceable, and they weigh health against what removal costs and what is technically feasible for a whole utility. EWG's guidelines carry no legal force. In EWG's own words, they are "based only on protecting health and does not consider technical feasibility or the cost of water treatment." EWG last updated its standards in February 2025.

So none of the multiples above is a violation. They show the distance between the legal standard and a stricter, health-only benchmark.

What a busy household can do

If the numbers are fine by you, nothing is required. If you would rather narrow the gap, here are the common choices, from least to most effort:

• Carbon pitcher or faucet filter. Cheap and quick. Mostly aimed at taste and odor, with results that vary by product and depend on changing the filter on time.
• Under-sink reverse osmosis (RO). A very fine membrane, installed once, treating the water you drink and cook with. RO is a common way to reduce dissolved contaminants such as disinfection byproducts.

The Sanavia Hydra is the tankless under-sink RO system we install across the DC area. In independent accredited lab testing of an Arlington, VA home's tap water, total trihalomethanes fell from 58 ppb to 2.79 ppb after the Hydra, a 95% reduction. The lab report is on our proof page.

Utility averages describe the system, not your faucet. A free water test gives you numbers for your own home, and we can mail a kit anywhere in the U.S. For the complete data set, see our Silver Spring, MD water quality report.