Enter your TDS meter reading to see how it compares with WHO taste bands and the US EPA guideline, convert it to EC, and find out what TDS can — and can't — tell you about your water.
Enter your TDS meter reading to compare it with WHO and EPA guidance and convert it to EC
Enter your TDS reading
TDS Reading
Meter Conversion Factor
Not sure? Leave it at 0.64. Check your meter's manual — many pens use 0.5, and hydroponic meters often use 0.5 ("500 scale") or 0.7 ("700 scale").
WHO Taste Scale (0 – 1200+ mg/L)
03006009001200+
⚠ Please enter a valid TDS reading greater than zero.
Your Results
TDS Level
—
ppm (mg/L)
EC Estimate (25 °C)
— μS/cm
In Parts per Thousand
— ppt
Factor Used
—
WHO Taste Band
—
vs EPA 500 mg/L
—
RO for Taste?
—
—
—
TDS doesn't tell you if water is safe. Bacteria, lead, arsenic and nitrate can all be present at low TDS. For safety, test for those specifically.
Visual TDS Meter
📖 How To Use
How to Use This TDS Water Calculator
Take a readingDip your TDS pen into a clean glass of water, stir gently to clear air bubbles, and wait for the number to settle. Rinse the probe with clean water between samples.
Enter the readingMost meters show ppm. For water, 1 ppm is the same as 1 mg/L, so either unit works.
Check the conversion factorYour meter actually measures conductivity (EC) and converts it with a factor. Leave it at 0.64 if you don't know — it only changes the EC figure, not the TDS rating.
Read the resultYou'll see where your reading sits in WHO's taste bands, whether it's above the US EPA 500 mg/L guideline, and the EC equivalent.
⚠️ Read This First
What TDS Can and Can't Tell You
A TDS meter adds up everything dissolved in the water into one number. It's useful for taste, scaling and checking a reverse osmosis filter — but it can't tell you whether water is safe to drink.
A TDS meter can show you
A TDS meter can't detect
How mineral-rich the water is
Bacteria and viruses
Likely taste and scaling
Lead, arsenic and most other toxic metals at harmful levels
Whether an RO filter is still working
Nitrate, pesticides and other specific contaminants
Sudden changes in a supply you know
Which substances make up the reading
Low TDS doesn't mean safe, and high TDS doesn't mean dangerous. Water at 80 ppm can contain harmful bacteria or lead; mineral water at 500 ppm can be perfectly safe. If you're on a private well or worried about your water, get a lab test for bacteria and the specific contaminants common in your area.
📐 The Formula
TDS Bands, Limits and Conversions
WHO taste bands for TDS
WHO hasn't set a health-based limit for TDS. Instead, it describes how the taste of water changes with TDS:
TDS (mg/L)
WHO taste rating
Below 300
Excellent
300 – 600
Good
600 – 900
Fair
900 – 1,200
Poor
Above 1,200
Unacceptable
WHO also notes that water with very low TDS can taste flat and insipid. The US EPA has a non-enforceable secondary standard of 500 mg/L, set for taste and to limit scaling and staining — not as a health limit.
Common factors: 0.50 (NaCl / "500 scale"), 0.64 (general), 0.70 ("700 scale")
Example: 320 ppm on a 0.64 meter = 320 ÷ 0.64 = 500 μS/cm
TDS meters measure conductivity and convert it using a fixed factor, usually referenced to 25 °C with automatic temperature compensation. The true factor depends on which minerals are dissolved, so a pen's TDS reading is an estimate — a lab measures TDS directly by evaporating the water and weighing what's left.
Parts per thousand
ppt = ppm ÷ 1,000 — e.g. 500 ppm = 0.5 ppt. Some meters switch to ppt at high readings.
🌊 Use Cases
What a TDS Meter Is Good For
🔬
Checking an RO Filter
Measure before and after your reverse osmosis unit. When the "after" reading starts creeping up, the membrane or filters need changing.
☕
Coffee & Tea
Mineral content affects extraction. The Specialty Coffee Association's water standard targets about 150 mg/L, with 75–250 mg/L acceptable.
🌿
Hydroponics
TDS or EC tracks nutrient strength. Follow your nutrient maker's EC chart for each crop and growth stage, and note which scale your meter uses.
🐠
Aquariums
TDS helps keep water consistent between changes. The right range depends on the species you keep.
🚿
Scale & Appliances
High-TDS water, especially hard water, leaves scale in kettles, heaters and pipes. See our water hardness calculator.
📈
Spotting Changes
A sudden jump in TDS from a supply you know well is a sign something has changed — worth a proper lab test.
❓ FAQ
Frequently Asked Questions
What is a good TDS level for drinking water?
For taste, WHO rates water below 300 mg/L as excellent and 300–600 mg/L as good. The US EPA's non-enforceable secondary standard is 500 mg/L, set for taste and scaling. Neither is a safety limit — TDS doesn't show whether water contains germs or toxic substances.
Can a TDS meter tell me if my water is safe?
No. TDS meters measure how much is dissolved in total, not what it is. They can't detect bacteria or viruses, and harmful substances like lead, arsenic and nitrate can be present at levels that barely change the reading. For safety, use a certified lab test for the contaminants that matter in your area.
What does TDS measure in water?
Total dissolved solids — mostly minerals such as calcium, magnesium, sodium and potassium, with bicarbonate, chloride and sulphate. It doesn't include suspended particles (turbidity) or living things like bacteria.
Is TDS the same as ppm?
ppm is the unit TDS is usually given in. For water, 1 ppm equals 1 mg/L. Some meters switch to ppt (parts per thousand) at high readings: 1 ppt = 1,000 ppm.
Is TDS the same as water hardness?
No. Hardness measures only calcium and magnesium. TDS includes those plus everything else dissolved, such as sodium and chloride. Water softened with salt can have high TDS but almost no hardness. To measure hardness, use a hardness test and our water hardness calculator.
What is the difference between TDS and EC?
EC (electrical conductivity, in μS/cm) is what the meter actually measures. It converts EC to TDS by multiplying by a factor — commonly 0.5, 0.64 or 0.7. That's why two meters can show different ppm for the same water. Hydroponics usually works in EC to avoid this confusion.
How do I lower TDS in my water?
Reverse osmosis is the usual household method and removes most dissolved solids. Distillation and deionisation also work. Carbon and sediment filters improve taste and clarity but barely change TDS. A water softener swaps calcium and magnesium for sodium, so TDS stays about the same.
Is very low TDS water bad for you?
Water from RO or distillation can taste flat, and WHO notes very low TDS can make water less acceptable to drink. Most of the minerals people need come from food, not water, but many RO systems add a remineralising stage for taste. If you're concerned about a specific diet or health condition, ask your doctor.
How accurate are TDS meters?
Good enough to compare readings and spot changes, but approximate as an absolute number. The meter's fixed conversion factor won't exactly match your water's mix of minerals, and dirty or scaled probes read wrong. Calibrate with a standard solution if accuracy matters, and use a lab for a true TDS measurement.
✅ Sources & Review
Sources and review
The bands and limits on this page come from these references:
Specialty Coffee Association water standard — target about 150 mg/L TDS for brewing.
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.
