SwiftPro Heating, Cooling and Plumbing(571) 396-0299

How hard is the water in Annandale?

The water in Annandale ran 3 to 10.8 grains per gallon in 2025, according to Fairfax Water. That's soft to very hard. Water like that leaves sediment in a tank water heater, so flush it once a year. A SwiftPro flush is $99, normally $199.

The water in Annandale, by the numbers

Water utilityFairfax Water
Hardness3 to 10.8 grains per gallon2025
What that isSoft to very hardU.S. Geological Survey classes
ZIP codes22003
How oftenFlush a tank once a yearDescale a tankless yearly too
Owner-occupied homes14,445half built before 1967

Source: Fairfax Water water quality report; U.S. Census Bureau, American Community Survey 2020 to 2024, median year built; U.S. Geological Survey, Hardness of Water.

What it means for your water heater

Hard water carries calcium and magnesium. Heat a tank of it and some drops out as sediment on the bottom, under the burner or the lower element. That's what makes a water heater rumble and pop, take longer to recover and wear out early. Flushing it once a year clears it out.

  • Popping or rumbling while it heats. That is water boiling under a layer of sediment.
  • Grit in the faucet screens on the hot side.
  • A drain valve nobody has opened since the house was sold.

A tankless gets descaled instead. Navien's manual calls for it once a year wherever the water runs 4 grains per gallon or harder with no softener, and the water in Annandale does. Descaling is $300, regularly $350.

Half the owner-occupied homes in Annandale were built before 1967. A house that age can still have its original shutoff valves and supply lines, which is why every flush comes with the plumbing safety check: supply hoses, shutoff valves, water pressure and drains, with photos of anything worth knowing about.

More on the flush in Annandale on SwiftPro's Annandale water heater flush page.

The rest of the water in Annandale

Hardness is one line of Fairfax Water's testing. The full Fairfax Water water report shows every contaminant it found, next to the legal limit and the health guideline. On a private well, a test at your own tap is the number that counts.

Nearby towns

Questions people ask

Is Annandale water hard?
Yes, soft to very hard. Fairfax Water reported 3 to 10.8 grains per gallon in 2025. The U.S. Geological Survey calls anything over 7 grains per gallon hard.
How often should I flush my water heater in Annandale?
Once a year for a tank. A tankless gets descaled once a year too, because the water in Annandale is over Navien's 4 grains per gallon line.
How much is a water heater flush in Annandale?
$99 at SwiftPro, normally $199, with the plumbing safety check included. Tankless descaling is $300, regularly $350. You pay after the visit.

Get it flushed for $99.

Normally $199, with the plumbing safety check included. Tankless descaling is $300, regularly $350. Pick a time online, and you pay after the visit.

Pick a timeCall (571) 396-0299