Your water comes down to two plants and a few numbers

WSSC Water quality numbers split by plant: the Potomac plant averaged 154 mg/L hardness in the 2025 report and the Patuxent plant averaged 70 mg/L.

Updated November 2, 2026

Every number in this section

• 154 mg/LHardness by plantPotomac plant average hardness, 2025; Patuxent plant averages 70 mg/L
• About 75%Which plant serves youof customers served by the Potomac plant
• Below 2 ppbLead in tap water90th-percentile lead, 69 sites; a system figure, not your tap
• About 1.1 pptPFAS numbersPotomac PFOS running annual average, 2025; EPA's limit is 4.0 ppt
• 10 linesThe tap report, line by linefrom the 2025 report, each shown for both plants
• 120°FWater heaters and scalethe water heater setting CPSC urges, to cut scald risk

This desk is independent of WSSC Water and isn’t a plumbing contractor. Each page below opens with one figure and says what that figure can’t tell you.

Start with the source

• Which plant serves you: about 75% of customers get the Potomac plant. Towns are a likely read only, so check the utility’s address map.
• Hardness by plant: 9.0 grains per gallon on Potomac and 4.1 on Patuxent, our arithmetic. Not every home needs a softener.
• The tap report, line by line: 10 lines for both plants, from sodium at 16 and 22 mg/L to nitrate at 0.8 and 1.0.

Then the numbers people worry about

• Lead in tap water: 90th-percentile lead below 2 ppb across 69 sites. That’s a system figure and it doesn’t test your house. The page has EPA’s steps.
• PFAS numbers: a Potomac PFOS running average of about 1.1 ppt against a 4.0 limit, and one 4.2 reading that needs explaining.

And the tank in the basement

• Water heaters and scale: 120°F is the CPSC setting. Hard water decides how much scale builds, and gas work is licensed work.

Your pipes affect the tap too. See who owns which pipe and how we check these figures.

Where each number comes from