📖 How To Use
How to Use This TDS Water Calculator
Getting your water quality assessment takes under 10 seconds:
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Take a TDS meter reading
Dip your TDS pen or digital meter into the water sample. Wait for the reading to stabilise — this usually takes 3–5 seconds. Rinse the probes with distilled water before testing to avoid contamination from previous samples.
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Enter the reading and choose the unit
Type your value into the TDS Reading field. Most meters display in ppm (parts per million). Since 1 ppm = 1 mg/L for water, both units are identical — select whichever your meter shows.
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Add water temperature (optional)
TDS readings are slightly temperature-dependent. Entering the water temperature allows the calculator to refine the electrical conductivity (EC) estimate. Leave blank to use the standard 25°C reference.
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Click Analyse Water Quality
Your results appear instantly — WHO quality rating, EPA compliance status, EC estimate, hardness classification, filter recommendation, and a suitability guide for drinking, aquariums, plants, and industrial use.
Tip: For the most accurate TDS reading, test water that has been sitting still for at least 5 minutes. Running water can introduce air bubbles which skew readings slightly upward. Also test at a consistent time of day — municipal water TDS can vary by 10–30 ppm across the day due to supply blending.
📐 The Formula
TDS Formula & Calculations Explained
TDS itself is measured directly by a meter — but the calculator derives several related values from your reading:
TDS and Electrical Conductivity (EC)
TDS and EC are closely related. EC measures how well water conducts electricity (a proxy for ion concentration), and TDS is estimated from it using a conversion factor:
TDS (ppm) ≈ EC (μS/cm) × 0.64
→ EC (μS/cm) = TDS (ppm) ÷ 0.64
The 0.64 factor (TDS factor) is the most common for general water testing.
Range: 0.50–0.70 depending on ion composition.
Salinity Estimate
Salinity (‰) ≈ TDS (ppm) × 0.001
e.g. 500 ppm TDS → ~0.5 ‰ (freshwater range)
WHO TDS Quality Bands
| TDS Range (ppm) | WHO Rating | Taste Description | Suitability |
|---|
| 0 – 50 | Excellent | Flat, slightly bland | Drinking, RO output |
| 50 – 150 | Excellent | Clean, neutral to slightly mineral | Ideal for drinking |
| 150 – 300 | Good | Pleasant mineral taste | Drinking water |
| 300 – 600 | Acceptable | Noticeable mineral flavour | Acceptable for drinking |
| 600 – 900 | Poor | Salty or bitter notes | Needs treatment |
| 900 – 1200 | Very Poor | Strongly salty/metallic | Not recommended for drinking |
| 1200+ | Unacceptable | Brackish / industrial | Requires purification |
TDS Suitability by Use Case
| Application | Recommended TDS (ppm) | Notes |
|---|
| Drinking water | 50 – 300 | WHO recommends <300 as good quality |
| Coffee & brewing | 75 – 250 | SCA recommends 75–150 for optimal extraction |
| Baby formula | <100 | Low mineral content recommended |
| Aquarium (freshwater) | 50 – 200 | Varies by fish species |
| Aquarium (marine) | 0 – 10 (RODI) | Use RO/DI water then add salt |
| Hydroponics | 560 – 840 | Nutrients raise TDS; adjust per crop |
| Irrigation / plants | <1000 | Most plants tolerate up to 1,000 ppm |
| Car washing / glass | <30 | Above 30 ppm causes spotting |
| Boiler / industrial | <100 | High TDS causes scale and corrosion |
🌊 Use Cases
When to Use a TDS Water Calculator
Knowing your water's TDS level is relevant in many everyday and professional situations:
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Drinking Water Safety
Verify that tap, filtered, or bottled water falls within WHO and EPA safe limits before consumption.
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Aquariums & Fishkeeping
Match TDS to the natural habitat of your fish. Discus and cardinal tetras need <150 ppm; African cichlids prefer 200–400 ppm.
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Hydroponics & Aquaponics
Monitor nutrient concentration in your reservoir. TDS directly reflects fertiliser levels — keep it in the crop's optimal range.
☕
Coffee & Tea Brewing
Water TDS affects extraction. The Specialty Coffee Association recommends 75–150 ppm for balanced, complex espresso.
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Industrial & Boiler Water
High TDS accelerates scale build-up in boilers, cooling towers, and heat exchangers — verify compliance before use.
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RO Filter Performance
Compare TDS before and after your reverse osmosis filter to verify rejection rate. A good RO removes 90–99% of TDS.
❓ FAQ
Frequently Asked Questions
What is a good TDS level for drinking water?
The WHO considers TDS below 300 ppm to be good quality for drinking water, and 50–150 ppm is considered ideal. The US EPA has set a secondary (non-enforceable) standard of 500 ppm as the maximum for aesthetic quality. Most people can taste a difference above 300–400 ppm.
What does TDS measure in water?
TDS (Total Dissolved Solids) measures the total concentration of all dissolved substances in water — including minerals like calcium, magnesium, sodium, and potassium, as well as chlorides, sulfates, bicarbonates, and trace metals. It does not measure bacteria, viruses, or turbidity. A high TDS reading can indicate mineral richness (not always harmful) or contamination (requires testing for specific ions).
Is TDS the same as ppm?
Yes — for water, TDS is almost always expressed in ppm (parts per million) or mg/L (milligrams per litre). These two units are numerically equivalent: 1 ppm = 1 mg/L. Some meters display in ppt (parts per thousand), which is 1,000× larger — a reading of 1 ppt = 1,000 ppm.
What is the difference between TDS and EC (electrical conductivity)?
EC measures the ability of water to conduct electricity, expressed in microsiemens per centimetre (μS/cm). TDS meters actually measure EC and then multiply by a conversion factor (typically 0.64) to estimate TDS in ppm. EC is more commonly used in hydroponics and agriculture, while TDS/ppm is the standard for drinking water testing.
How do I lower TDS in my water?
The most effective methods to reduce TDS are: Reverse Osmosis (RO) — removes 90–99% of dissolved solids; Distillation — boiling and condensing removes virtually all TDS; Deionisation (DI) — ion exchange resins reduce TDS to near zero; and Nanofiltration — removes multivalent ions while retaining some minerals. Regular carbon or sediment filters do not meaningfully reduce TDS.
Can water with low TDS (under 50 ppm) be harmful?
Very low TDS water (such as RO-purified or distilled water below 10–20 ppm) lacks essential minerals and can taste flat. Some research suggests that drinking demineralised water long-term may leach minerals from the body, though this is disputed. For drinking, a TDS of 50–150 ppm is generally considered ideal, providing a good mineral balance. Water below 50 ppm is typically remineralised before bottling or household use.
How accurate are TDS meters?
Most consumer TDS pens claim ±2% accuracy. In practice, accuracy depends on: the TDS conversion factor used (varies by ion type), electrode condition (scale or contamination reduces accuracy), and calibration. For precise measurements, use a laboratory-grade EC meter with accurate TDS factor for your water source, or send a sample for full ICP-MS mineral analysis.
What TDS should I target for hydroponics?
In hydroponics, TDS reflects nutrient solution strength. General targets by growth stage: seedlings 100–250 ppm, vegetative growth 800–1,200 ppm, flowering/fruiting 1,200–1,800 ppm. Start with your source water's base TDS, subtract it from the target, then add nutrients to make up the difference. Different crops have different optimal ranges — leafy greens tolerate 560–840 ppm, while tomatoes prefer 1,400–3,500 ppm.