TDS in Well Water: What Total Dissolved Solids Mean
TDS (Total Dissolved Solids) is one of the most common water quality measurements, and well owners often wonder what their numbers mean. TDS indicates the concentration of dissolved substances in water—minerals, salts, metals, and organic matter. While not a direct health concern, TDS affects taste, appliance longevity, and overall water quality.
đź“‹ In This Guide
This guide explains what TDS measures, normal ranges for well water, what causes high readings, and when treatment makes sense.
Need your well water tested? We provide comprehensive water quality analysis including TDS and specific mineral content.
Call (760) 440-8520What Does TDS Measure?
TDS represents the total concentration of dissolved inorganic salts and organic matter in water. It includes:
- Minerals: Calcium, magnesium, potassium, sodium
- Anions: Chlorides, sulfates, bicarbonates, nitrates
- Metals: Iron, manganese, zinc (trace amounts)
- Other: Silica, organic compounds
TDS is measured in mg/L (milligrams per liter) or ppm (parts per million)—these are equivalent: 1 mg/L = 1 ppm.
How TDS is Measured
TDS meters: Electronic meters measure electrical conductivity (EC). Pure water doesn't conduct electricity; dissolved solids do. The meter converts EC to estimated TDS. Quick and affordable ($10-50 for basic meters).
Laboratory testing: More accurate. Water is evaporated; residue is weighed. Also provides breakdown of specific minerals.
Limitation: TDS meters give a total number but don't tell you what's in the water. High TDS could be harmless calcium or concerning nitrates—you can't tell without further testing.
TDS Levels and What They Mean
| TDS Level (ppm) | Rating | Notes |
|---|---|---|
| 0-50 | Very low | Unusual for well water; may indicate RO treated or very soft water |
| 50-150 | Low | Excellent quality; minimal mineral content |
| 150-300 | Good | Ideal range for drinking; some beneficial minerals |
| 300-500 | Fair | Common for well water; EPA recommended limit is 500 |
| 500-1000 | High | May have taste issues, scaling; treatment often beneficial |
| 1000-2000 | Very high | Noticeable taste; treatment recommended |
| 2000+ | Brackish | Generally requires treatment for household use |
EPA Guidance
The EPA's secondary (aesthetic) standard for TDS is 500 mg/L. This isn't a health-based limit—it's based on taste and cosmetic effects. There's no primary (health) standard for TDS because the concern depends on what makes up the TDS.
What Causes High TDS in Well Water?
Natural Sources
- Geology: Wells in limestone, shale, or mineral-rich formations naturally have higher TDS
- Deep wells: Older, deeper groundwater often has higher mineral content
- Coastal areas: Saltwater intrusion raises TDS significantly
- Arid regions: Less rainfall means less dilution of minerals
Human-Caused Sources
- Agricultural runoff: Fertilizers, pesticides
- Septic systems: Nitrates, chlorides
- Road salt: Winter de-icing
- Industrial discharge: Various contaminants
Why TDS Changes
If your TDS has increased over time, consider:
- Drought: Groundwater becomes more concentrated
- Overpumping: Drawing from lower, more mineralized zones
- Saltwater intrusion: Coastal wells drawing seawater
- Nearby contamination: New septic systems, agricultural changes
- Well depth changes: Deepening accesses different water
Health Considerations
TDS Itself
There's no evidence that high TDS itself poses health risks. In fact, some mineral content is beneficial—calcium and magnesium in water contribute to daily intake.
What High TDS Can Indicate
While TDS itself isn't harmful, high TDS may indicate the presence of specific contaminants that are concerning:
- Nitrates: Health concern at >10 ppm (particularly for infants)
- Sulfates: Laxative effect at high levels
- Sodium: Concern for sodium-restricted diets
- Arsenic, lead, other heavy metals: Potential health hazards
Important: If TDS is high, get a detailed water test to identify specific components—TDS alone doesn't tell the whole story.
Very Low TDS
Some people assume lower is better, but extremely low TDS water (like RO or distilled) may:
- Taste flat or "empty"
- Be slightly more corrosive to pipes
- Lack beneficial minerals
This isn't a significant health concern but is worth noting.
Effects of High TDS
Taste and Odor
- 500-1000 ppm: May notice mineral taste
- 1000+ ppm: Often described as salty, bitter, or metallic
- Specific minerals affect taste differently (sulfates taste bitter, sodium tastes salty)
Scale and Deposits
- Hard water (calcium/magnesium) causes scale
- White deposits on fixtures, dishes
- Reduced appliance efficiency and lifespan
- Clogged pipes over time
Appliances
- Water heaters work harder, fail sooner
- Dishwashers leave spots
- Coffee makers clog
- Humidifiers produce white dust
Plumbing
- Scale buildup reduces pipe diameter
- Lower water pressure over time
- Fixture aerators clog
TDS Treatment Options
Reverse Osmosis (RO)
Most effective TDS reduction:
- Removes 90-99% of dissolved solids
- Point-of-use (under sink) most common for drinking water
- Whole-house RO available but expensive
- Produces some wastewater (reject water)
Cost: $150-500 (under sink); $1,500-5,000+ (whole house)
Water Softener
Addresses hardness component of TDS:
- Exchanges calcium/magnesium for sodium
- Reduces hardness but adds sodium (net TDS stays similar)
- Eliminates scale problems
- Doesn't reduce other TDS components
Cost: $800-2,500+ installed
Distillation
Effective but limited:
- Removes virtually all TDS
- Energy-intensive
- Slow production rate
- Mainly practical for drinking water
Deionization
Specialty use:
- Removes dissolved minerals via ion exchange resins
- Produces very pure water
- Resin requires regeneration/replacement
- Not common for residential whole-house
When to Treat High TDS
Consider treatment if:
- TDS >500 ppm AND taste is objectionable
- Scaling is causing problems
- Specific contaminants are identified
- You prefer mineral-free drinking water
May not need treatment if:
- TDS is 300-500 ppm with no taste issues
- No specific contaminants of concern
- Scaling is manageable
Many people drink well water at 400-600 ppm without complaint. Treatment is about preference and specific water chemistry, not just the TDS number.
Frequently Asked Questions
What is a good TDS level for well water?
The EPA recommends TDS below 500 mg/L (ppm) for drinking water. Levels between 300-500 ppm are common and acceptable for well water. Below 300 ppm is considered excellent. Above 500 ppm may have aesthetic issues (taste, scaling), and above 1000 ppm is generally unpalatable without treatment. The ideal range for taste is typically 150-300 ppm.
Is high TDS water safe to drink?
TDS itself is a secondary (aesthetic) standard, not a health standard. High TDS water is generally safe unless specific harmful contaminants are present. However, high TDS often indicates hardness, sulfates, or other minerals that affect taste, cause scaling, and may have laxative effects at very high levels. If TDS is elevated, get a detailed test to identify what's in the water.
How do I lower TDS in my well water?
Reverse osmosis (RO) is the most effective TDS reduction method, removing 90-99% of dissolved solids. Under-sink RO systems are affordable ($150-500) for drinking water. Water softeners reduce hardness (part of TDS) but add sodium, so net TDS stays similar. Distillation also removes TDS but is energy-intensive and slow. For whole-house TDS reduction, large RO systems exist but are expensive.
Why did my well water TDS increase?
Rising TDS can indicate: drought conditions concentrating minerals, saltwater intrusion in coastal areas, septic or agricultural contamination nearby, natural changes in aquifer chemistry, or well depth changes accessing different water. A significant increase warrants investigation—get a full water quality test to identify what's elevated and potential sources.
Does a TDS meter tell me if water is safe?
No. TDS meters measure total dissolved solids but don't identify what those solids are. High TDS could be harmless calcium or dangerous arsenic—you can't tell without laboratory testing. TDS meters are useful for monitoring changes over time and checking filter performance, but they don't replace proper water quality testing.
What's the difference between TDS and hardness?
Hardness specifically measures calcium and magnesium. TDS measures all dissolved solids including hardness plus sodium, chlorides, sulfates, etc. You can have high TDS but low hardness (high sodium water) or moderate TDS with high hardness (limestone aquifer). Water softeners reduce hardness but may not change overall TDS much.
Get Your Water Tested
A TDS reading is just one piece of the puzzle. Southern California Well Service provides comprehensive water testing that identifies exactly what's in your water and what treatment makes sense.
Call (760) 440-8520Licensed C-57 Contractor | San Diego, Riverside & San Bernardino Counties
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