Silver Spring water spans 58 to 213 mg/L and concentrates at late-summer Potomac low flow, while pine, oak and cherry pollen overlap through spring.
Silver Spring's water depends on the WSSC plant behind the tap: Patuxent water averages 70 mg/L and Potomac water 154, the difference between moderately hard and hard, and the Potomac side climbs further at late-summer low flow. Pine, oak and cherry pollen overlap in spring, and downtown frontage takes traffic and construction film. Book April or August to October; a single-story exterior runs $300 to $550, and the NOAA and Discovery offices keep commercial crews on contract.
WSSC treats Potomac and Patuxent water at two separate plants, and its 2025 tap water analysis shows how much that matters: Patuxent water averages 70 mg/L (58 to 86) and Potomac water 154 (79 to 213). The practical consequence for a crew is that the DC metro contains at least three distinct supplies: WSSC's two rivers, the federal Washington Aqueduct across the state line, and Coastal Plain groundwater to the south.
Figures by plant, as reported.
| Hardness | 58–213 mg/L as CaCO₃ 70 on average from the Patuxent plant and 154 from Potomac, so the plant serving an address matters more than any single figure, as published by Washington Suburban Sanitary Commission. |
|---|---|
| pH | 7.3–7.5 |
| Alkalinity | 38–83 mg/L as CaCO₃ |
| Iron | 0–0.65 mg/L |
| Manganese | 0–0.094 mg/L |
| Sodium | 16–22 mg/L |
| Chloride | 43–51 mg/L |
| Disinfectant | uv + chlorine |
| Source and treatment | Potomac River water and Patuxent reservoir water on the WSSC system; which plant serves an address decides the delivered chemistry · Algae control, powdered activated carbon and permanganate, coagulation, flocculation, rapid mix, lime and soda ash, sedimentation and rapid sand filtration, ultraviolet radiation and chlorination, fluoridation, with an orthophosphate inhibitor and pH adjustment · The plant softens. |
Not in the report: corrosion index and total dissolved solids.
SOURCE · WSSC Water 2025 Tap Water Analysis Report, Potomac and Patuxent Water Filtration Plants, general water quality and inorganics tables · How we source these numbers
Late-summer low flow on the Potomac concentrates whatever the river carries, so the mineral end of the year lands in August and September rather than spring. Overlaid on that is an unusually long pollen sequence for the latitude — pine, oak and cherry in overlapping waves through the spring, with the cherry component peaking early and the pine dominating by volume.
MARYLAND SEASON BY SEASON →WSSC supplies Silver Spring from the Potomac and Patuxent through two plants and publishes hardness for each: 70 mg/L on average from Patuxent and 154 from Potomac, so the plant serving an address decides whether the water is moderately hard or hard. The DC metro holds at least three distinct supplies that are routinely confused. Potomac low flow puts the mineral peak in late summer rather than spring, and Takoma Park's conservation-district Victorian glazing is the skilled end of the residential book.
WSSC supplies Silver Spring from the Potomac and the Patuxent through two separate treatment plants, and the commission publishes hardness per plant: 70 mg/L on average at Patuxent, 154 at Potomac. Two plants on two rivers produced per-plant publication here, as it has in every comparable system checked.
Closing WSSC would be one of the largest single unlocks still open on this site. It serves roughly 1.8 million people across Montgomery and Prince George's counties, so one read would settle Silver Spring, Germantown and every other WSSC address at once.
The DC metro contains at least three distinct supplies and they are routinely confused. WSSC takes the Potomac and the Patuxent; Arlington and the other Washington Aqueduct jurisdictions are on a separate federally operated system drawing the same river; Southern Maryland runs on Coastal Plain groundwater. A figure from one says nothing about the others.
Potomac low flow in late summer concentrates whatever the river carries, so the mineral end of the year arrives in August and September rather than in spring. That inverts the usual expectation and it is worth explaining to customers who book their annual clean in May.
The spring pollen sequence here is unusually long for the latitude, with pine, oak and cherry overlapping. Cherry peaks early and pine dominates by volume, and the combined load needs a presoak rather than a dry first pass.
Takoma Park's Victorian stock sits inside a residential conservation district, with leaded, stained and wavy single-pane glass in original sash. The district's expectations constrain method before the glazing does, and that is the skilled end of an otherwise straightforward residential market.
The federal and media cluster downtown — NOAA, Discovery and the agencies around them — provides a contracted commercial book with security scheduling and fixed standards, and that is what makes the market stable rather than seasonal. Takoma Park heritage work supports a conservation rate at the other end, with little in between.
Takoma Park is where this stops being ordinary. Its Victorian stock sits in a residential conservation district with leaded, stained and wavy single-pane glass in original sash, and the district's own expectations constrain method before the glass does. The downtown towers are rope-and-stage work. Between those, the post-war housing is genuinely approachable.
OPEN COST ESTIMATOR →2025 annual mean at the Mcmillan NCore-Pams monitor, 2500 1ST Street, N.W. Washington DC, 9 km south of the city (EPA site 11-001-0043).
Silver Spring sits in WSSC's service area, and WSSC issues the hydrant meter and fittings to anyone holding its temporary hydrant permit. The holder must pick that equipment up within ten business days and return it by the permit's expiry; late return can mean a forfeited deposit, the meter being pulled, refusal of future permits, or criminal prosecution.
WSSC Code of Regulations §3.57.080: approved hydrant permit holder responsibilities · checked September 2026
Silver Spring falls under Montgomery County's code, which makes it illegal to put any pollutant into the county's streams and other state waters, directly or by storing or applying it where rain will carry it off, unless a discharge permit, a compliance plan or approved best management practices cover it. Keep soapy wash water out of the street inlets.
Montgomery County Code Sec. 19-50: prohibition of water pollution · checked September 2026
Silver Spring sits in unincorporated Montgomery County, where changing the exterior of a designated historic site, or of a resource inside a county historic district, first needs an historic area work permit under the county's historic preservation chapter. Ordinary maintenance is the stated exception.
Montgomery County Code Sec. 24A-6: historic area work permits, generally · checked September 2026
Wet-only handling. Peak early-to-mid April. Pollen lifts cleanly with water plus light alkaline soap; do not scrape. Annapolis tidal-basin cherry-blossom adjacent properties hit hardest.
When the Potomac drops in late summer, WSSC supply mineral concentration rises and scale deposition on glass increases. Extended citric dwell required during these windows. Same pattern Tony Petruzzi documents for Northern Virginia DC-metro.
WSSC treats Potomac and Patuxent water at two separate plants, and its 2025 tap water analysis shows how much that matters: Patuxent water averages 70 mg/L (58 to 86) and Potomac water 154 (79 to 213).
Residential window cleaning in Silver Spring typically runs $10–16 per pane or $300–550 for a standard single-story exterior. The federal and media cluster downtown — NOAA, Discovery and the agencies around them — provides a contracted commercial book with security scheduling and fixed standards, and that is what makes the market stable rather than seasonal.
Silver Spring's drier, frost-free months are April and August to October, by NOAA's 1991–2020 normals for the Beltsville station, where May brings the most rain. The calendar on this page marks August (after the April 16 bloom), September (after smoke season) and October (before frost). Frost nights usually run from November 1 to April 10.
Not as the final rinse: Washington Suburban Sanitary Commission publishes hardness of 58–213 mg/L, enough to spot as it dries, so finish with pure water. Its iron, up to 0.65 mg/L, is at the staining level, and acid cleaners will not lift that film. It draws on Potomac River water and Patuxent reservoir water on the WSSC system.
In Silver Spring the dominant residue patterns include late-summer potomac low-flow mineral concentration and overlapping pine, oak and cherry pollen through spring. Late-summer low flow on the Potomac concentrates whatever the river carries, so the mineral end of the year lands in August and September rather than spring.
Takoma Park is where this stops being ordinary. Its Victorian stock sits in a residential conservation district with leaded, stained and wavy single-pane glass in original sash, and the district's own expectations constrain method before the glass does. The downtown towers are rope-and-stage work. Between those, the post-war housing is genuinely approachable.
Post-2000 mixed-use high-rise core with substantial IGU and curtain-wall stock. Woodside Park and Takoma Park have their own housing stock and glazing as well.
Just over the Maryland line