Total dissolved solids (TDS) measures all inorganic and organic substances dissolved in water. The EPA's secondary standard is 500 mg/L. Phoenix tap water averages 400-650 mg/L, often above that aesthetic threshold. Below 300 mg/L is "excellent" per WHO. Above 1,000 mg/L is generally unfit for drinking. Reverse osmosis is the only home technology that reliably reduces TDS.
What Is TDS in Drinking Water?
Total dissolved solids (TDS) is the combined concentration of all inorganic salts, minerals, metals, and small amounts of organic matter dissolved in a sample of water, measured in milligrams per liter (mg/L) or parts per million (ppm). The most common dissolved constituents in Arizona tap water are calcium, magnesium, sodium, potassium, bicarbonates, sulfates, chlorides, and nitrates. A handheld TDS meter does not identify which substances are present, only their cumulative electrical conductivity converted to a mg/L estimate.
TDS is the single most useful "snapshot" reading for evaluating drinking water because it correlates with hardness, taste, scale potential, and the presence of dissolved contaminants. The EPA places TDS on its National Secondary Drinking Water Regulations list, meaning it affects taste, odor, and appearance rather than acute health. Aquafeel Solutions Arizona measures TDS during every free in-home test using a calibrated digital conductivity meter.
EPA, WHO, and NSF TDS Standards
The U.S. Environmental Protection Agency sets a Secondary Maximum Contaminant Level (SMCL) of 500 mg/L for TDS. Above this level, water tends to taste salty, metallic, or bitter, and accelerates scale buildup in pipes, fixtures, and appliances. The World Health Organization uses a five-tier palatability scale, and NSF International certifies reverse osmosis systems specifically for TDS reduction performance under Standard 58.
| TDS Level (mg/L) | WHO Rating | Notes |
|---|---|---|
| Less than 300 | Excellent | Best taste, minimal scale |
| 300 - 600 | Good | Typical for treated municipal supplies |
| 600 - 900 | Fair | Detectable taste, scale buildup likely |
| 900 - 1,200 | Poor | Salty/bitter taste, treatment recommended |
| Over 1,200 | Unacceptable | Not recommended for daily drinking |
Sources: EPA Secondary Drinking Water Standards (40 CFR 143.3); WHO Guidelines for Drinking-Water Quality, 4th edition.
Typical TDS Levels in Arizona Tap Water
Phoenix-area tap water typically tests between 400 and 650 mg/L TDS, putting much of the metro at or above the EPA's 500 mg/L aesthetic limit. The variation comes from the changing blend of source waters: Salt River Project surface water averages around 350 mg/L, Central Arizona Project (CAP) Colorado River water averages 600-700 mg/L, and groundwater wells can exceed 800 mg/L in older aquifers. Tucson, which recharges CAP water into its aquifer before delivery, averages 350-500 mg/L.
TDS by Phoenix-Metro City
- Phoenix: 450 - 600 mg/L (per 2025 City of Phoenix CCR)
- Mesa: 500 - 650 mg/L
- Chandler: 480 - 620 mg/L
- Gilbert: 500 - 640 mg/L
- Scottsdale: 470 - 600 mg/L
- Glendale: 520 - 680 mg/L
- Tucson: 350 - 500 mg/L
Source: 2025 Consumer Confidence Reports published by each municipal water provider.
Health and Aesthetic Effects of High TDS
TDS itself is not a direct health hazard, but elevated TDS often signals high concentrations of specific constituents that are regulated for health, including nitrate, arsenic, fluoride, sodium, and sulfate. The WHO recommends testing individual constituents whenever TDS exceeds 600 mg/L because the source of the dissolved material matters more than the total. Aesthetic effects appear well below health thresholds.
Common signs of high TDS in Arizona homes include water that tastes "flat" or salty, rapid limescale buildup on glassware and faucets, white spots on dishes after the dishwasher cycle, and coffee or tea that tastes bitter or muddy. Above 1,200 mg/L, the WHO classifies water as "unacceptable" for daily drinking.
Specific Health-Regulated Components Bundled Inside TDS
- Sodium: EPA advisory of 20 mg/L for low-sodium diets, often elevated by softeners
- Nitrate: Federal MCL of 10 mg/L, particularly relevant for well water
- Arsenic: Federal MCL of 10 ppb, naturally occurring in some Arizona aquifers
- Sulfate: Secondary standard of 250 mg/L, causes laxative effect at higher levels
- Chloride: Secondary standard of 250 mg/L, contributes to corrosion
How to Test TDS in Your Home
The simplest way to test TDS at home is with a $15-30 handheld digital meter that displays a reading in seconds. Calibrate the meter against a 342 mg/L NaCl reference solution before first use, then dip the probe into a clean glass of room-temperature tap water. For confirmation against your municipal report, also pull the latest Consumer Confidence Report (CCR) from your water provider. Aquafeel Solutions Arizona brings calibrated meters to every free home test, along with hardness, chlorine, and pH analyzers.
How to Reduce TDS in Arizona Tap Water
Reverse osmosis (RO) is the only point-of-use technology that reliably reduces TDS by 90 to 99 percent, certified under NSF/ANSI Standard 58. A typical four- or five-stage under-sink RO unit pushes pre-filtered water through a semipermeable membrane that rejects nearly all dissolved solids, then stores treated water in a small tank for on-demand use. Whole-home softeners do not reduce TDS, they only swap calcium and magnesium for sodium ions across a resin bed.
TDS Reduction Methods Compared
- Reverse osmosis (RO): Removes 90-99% of TDS. Best for drinking and cooking water.
- Distillation: Removes 99% of TDS. Slow and energy intensive, rarely used at home.
- Deionization (DI): Removes 99% of TDS. Used in labs and specialty applications.
- Carbon filtration: Removes 0% of TDS. Targets chlorine, taste, and odor only.
- Water softening: Removes 0% of TDS. Swaps minerals, doesn't reduce total.
For a complete treatment recommendation tailored to your address and water source, schedule a free in-home test. Aquafeel Solutions Arizona specializes in dual-tank softener plus RO combinations engineered for Arizona's high-TDS conditions. See Water Softener vs Water Purifier for the full comparison.
Frequently Asked Questions
What TDS level is "ideal" for drinking water?
The WHO considers TDS below 300 mg/L "excellent" and 300-600 mg/L "good." Most bottled spring waters fall in the 50-300 mg/L range. Reverse osmosis systems typically produce 5-50 mg/L TDS water at the tap.
Can low TDS water be unhealthy?
Pure RO water (under 50 mg/L) is safe to drink, though some research, including a 2019 WHO review, suggests very long-term consumption of demineralized water may slightly increase mineral demand from food. Most U.S. health bodies consider any TDS below 500 mg/L safe.
Does boiling water reduce TDS?
No. Boiling kills microorganisms but actually concentrates TDS as water evaporates. To reduce TDS at home, you need reverse osmosis, distillation, or deionization.
How often should I test my home's TDS?
At least once a year, or whenever you notice taste changes, scale increases, or a switch in your provider's source-water blend. Aquafeel Solutions Arizona offers free annual checkups for installed customers.
Test Your TDS for Free at Home
Aquafeel Solutions Arizona brings calibrated TDS, hardness, chlorine, and pH meters to your door. The full test takes 15 minutes and includes a written report.
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