McLean is on Fairfax Water. Some customers get its own Potomac and Occoquan water and some get Potomac water treated by the Washington Aqueduct, and Fairfax Water's plant analyses show hardness from about 70 to 185 mg/L. In large homes with several bathrooms, that scale adds up quickly. Call the number on this page to be connected with a local plumber in McLean.

McLean water conditions
Fairfax Water says most of its customers receive water from its own treatment plants on the Potomac River and the Occoquan Reservoir, while some receive Potomac water treated by the Washington Aqueduct at the Dalecarlia and McMillan plants. Which supply reaches a given McLean street isn't something to guess, so a test at the tap is the honest starting point. Fairfax Water's Potomac plant runs from about 70 to 185 mg/L, roughly 4 to 11 grains per gallon.
The median McLean home dates to about 1976, but the area mixes postwar ramblers with large newer houses. Bigger homes often have two water heaters, multiple showers with rain heads and body sprays, and high peak flow. That pushes the softener toward larger valves and resin tanks so pressure doesn't drop when several fixtures run at once.
| Home type | Typical softener setup | Watch for |
|---|---|---|
| Older rambler, one water heater | Single-tank unit sized to household use | Old gate valves at the main that may not seal |
| Large home, several baths | High-flow valve, larger resin tank, or twin tanks | Pressure drop at peak use |
| Home with irrigation | Softener with irrigation teed off upstream | Backflow assembly that needs yearly testing |
Signs to look for
- Scale on glass shower enclosures and stone counters
- Showerheads and body sprays losing flow
- Tankless heaters throwing scale or flow error codes
- An older softener that runs out of soft water when guests stay
- Spots on dark stone, tile or a car washed with the house water
What the plumber needs to know
When you call, describe the number of bathrooms and water heaters, whether there's a tankless unit, and where the main enters the house. In many McLean basements the main, water heater and a floor drain sit close together, which keeps the install simple. In finished lower levels the plumber may need an access panel or a short reroute to reach the line.
Timing notes
Fairfax Water normally uses chloramines from July through March and free chlorine from April through June. Spring is when people notice taste most; a carbon stage handles that, not the softener. Lawn irrigation in Fairfax County needs a testable backflow assembly checked every year, so if you're rerouting lines in that area, plan both at once. Fairfax County Land Development Services is the permit office for McLean; it requires permits for new or relocated plumbing.
Water Softeners & Filtration questions in McLean
How hard is the tap water at my address?
Will a softener help my water heater or tankless unit last?
Should outdoor spigots and irrigation skip the softener?
Do I need a permit to put in a water softener?
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