What is Rockville water hardness in grains per gallon?

Rockville's water hardness is 3.6 grains per gallon (GPG), equivalent to 61 parts per million (PPM). 1 GPG = 17.1 PPM.

Water Quality in Rockville, MD

Rockville's water quality is good overall. Hardness is low at 61 PPM, and no contaminants exceed health guidelines. Most homes here do not need a water softener.

WSSC Water · Source: Potomac River · Serves 68,401 residents

Hardness (PPM)

TDS (PPM)

1.1

Chlorine (mg/L)

PFAS (ppt)

Lead (ppb)

Hardness Scale: Where Rockville Falls

Soft 060120180250400+

Generally good quality

Rockville receives WSSC Water from the Potomac River. The Piedmont-sourced water is moderately soft.

What Rockville's Water Means for Your Home

Rockville's water is moderately hard at 61 PPM. At this level, hard water is not a significant concern for most households. Scale buildup is minimal, and a water softener would provide little measurable benefit. If you are considering water treatment in Rockville, focus on contaminant filtration rather than softening.

Beyond hardness, Rockville's water quality is generally within EPA guidelines for regulated contaminants. Chlorine is present at 1.1 mg/L as a disinfectant residual, which is normal for municipal water systems. If you notice a pool-like taste or experience dry skin, a whole-house carbon filter is the most common and affordable solution. For homeowners who want to understand the full picture, requesting your utility's annual Consumer Confidence Report provides neighborhood-level data.

Contaminant	Detected	Health Guideline	Legal Limit	Status
Hardness (as CaCO₃)	61 PPM	< 60 PPM	No federal limit	✓ OK
Total Dissolved Solids	99 PPM	< 300 PPM	500 PPM	✓ OK
PFAS (total)	4 ppt	4 ppt (EPA)	4 ppt (2024)	✓ OK
Lead	3 ppb	0 ppb (no safe level)	15 ppb (action level)	✓ Low
Chlorine / Chloramine	1.1 mg/L	Taste threshold ~1.0	4.0 mg/L	✓ Normal
Nitrate	1 mg/L	5 mg/L	10 mg/L	✓ OK

Recommendations for Rockville Homes

🔄 Salt-Free Conditioner (Optional)

At 61 PPM, Rockville's water is moderately hard. Scale buildup is slow but noticeable over years, especially in tankless water heaters. A salt-free conditioner is a low-maintenance option if you want to extend appliance life.

Learn more about this solution →

About Rockville's Water Supply

Water Utility: WSSC Water

Water Source: Potomac River

Population Served: 68,401

Hardness: 61 PPM (3.6 grains per gallon)

Water quality can vary by neighborhood and season. The values above represent typical averages reported by WSSC Water. To get exact numbers for your address, request a copy of the most recent Consumer Confidence Report (CCR) from your utility, or have your water independently tested.

Compare Rockville to Other Maryland Cities

Frequently Asked Questions About Rockville Water

Is Rockville tap water safe to drink?

Rockville's water meets EPA legal standards for drinking water safety. However, legal limits and health-optimal levels are different things. Review the contaminant table above for specific numbers and how they compare to both legal limits and health guidelines.

Do I need a water softener in Rockville?

At 61 PPM, Rockville's water is moderately hard. Some homeowners at this level do not notice problems, while others see spotting on glassware, film on shower doors, or reduced soap lathering. Homes with tankless water heaters at this hardness level should strongly consider at least a salt-free conditioner, as scale buildup inside the heat exchanger can void the warranty. For other homes, it depends on your sensitivity and fixtures.

What water filter is best for Rockville?

The best filter depends on which contaminants you want to address. See our softener vs. filter guide to understand the difference between these categories.

Where does Rockville's water come from?

Rockville's drinking water is sourced from Potomac River and treated by WSSC Water. Rockville receives WSSC Water from the Potomac River. The Piedmont-sourced water is moderately soft.

What is the hardness of Rockville water in grains per gallon?

Rockville's water hardness is 3.6 grains per gallon (GPG), which equals 61 parts per million (PPM). This is classified as moderately hard. To convert: 1 GPG = 17.1 PPM.

Does Rockville water damage tankless water heaters?

At 3.6 GPG, Rockville's water is unlikely to cause significant issues for tankless water heaters. However, if you notice reduced flow or efficiency over time, scale buildup could be a factor. Annual flushing with vinegar is good maintenance regardless of hardness.

Is Rockville water safe for babies and infants?

Rockville's water meets all EPA safety standards and is generally considered safe for preparing infant formula. The hardness minerals (calcium and magnesium) are not harmful. If your home has older plumbing, running cold water for 30 seconds before use is a good precaution to flush any lead from pipes.

Data sources. Water quality data compiled from EPA SDWIS, EWG Tap Water Database, USGS water hardness studies, and the WSSC Water Consumer Confidence Report. Hardness and contaminant levels represent typical average values and may vary by neighborhood and season. Last updated: 2026-02-12.