Product dossier · What’s actually in your water · A TDS science dossier
Water has a number. Most people have never checked it.
Total Dissolved Solids is the single measurement that tells you how much is actually dissolved in the water you drink — minerals, salts, and, at the extremes, contaminants. This book lays out where the real thresholds sit, and why.
Tattwas Digital TDS Meter · Pocket Water Tester · Button-Cell Powered · Instant PPM Readout · HOLD Function · Pen Design · 6-Month Warranty
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100–300ppm range most water-quality sources recommend
5 tierson the WHO taste-panel palatability scale
<10 secto a reading — dip, wait, read
01 · Key benefits
Six reasons it earns a spot in the drawer.
Everything a pocket TDS pen should do — and nothing it pretends to. A fast, repeatable read on your water, honest about where its usefulness ends.
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Instant ppm reading
Dip the probe, wait a couple of seconds, and read the result — a clear digital TDS value in parts per million, on screen in under ten seconds.
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See what your filter really does
Compare tap, filtered, and RO output side by side. Find out whether your system is stripping too much or leaving too much behind.
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HOLD to capture the reading
Freeze a value on screen so you can note it down before it settles or changes — useful when you’re logging several sources in a row.
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Pocket-sized pen
Slim enough to live in a kitchen drawer or slip into a travel bag — so you can check hotel taps, a friend’s RO, or bottled water on the go.
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Button-cell powered
A long standby life suited to occasional daily use. No charging cable to keep track of — pick it up, take the reading, cap it, put it back.
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Evidence-based, not oversold
A screening signal for whether water is worth investigating further — with a booklet that’s clear about what a single number can and can’t tell you.
02 · Why a TDS meter
You filter it, boil it, buy it bottled — but you’ve never measured it.
Water quality is invisible. So most of us trust an RO system, a filter, or a bottled brand on faith — with no number to check it against.
TDS is that number. It’s the combined weight of everything dissolved in a litre of your water — the calcium and magnesium your body actually uses, and, at the other end, the salts and contaminants you’d rather know about.
Too low, and water can be stripped of minerals worth having. Too high, and taste, scale, and safety questions start to matter. Either way, the only way to know which side your water sits on is to measure it.
A handheld meter turns that invisible property into a reading in seconds — on any tap, filter, RO unit, or bottle you can dip it into.
One unit, spelled two ways: mg/L = ppm
TDS is expressed in milligrams per litre (mg/L), which is functionally identical to parts per million (ppm). One milligram per litre equals one part per million — so a reading of 247 mg/L and 247 ppm mean the same thing.
What one reading tells you
- Whether your water leans mineral-rich or mineral-poor
- Whether an RO or filter is over- or under-stripping minerals
- Whether a change in tap or bottled source is worth a closer look
- A useful first signal — not a full safety certificate on its own
| Without a meter | With a meter |
|---|---|
| You guess. You trust the label, and hope the filter is doing its job. | You know. A number you can track, compare, and act on. |
03 · How it works
It doesn’t weigh your water. It listens to it.
A TDS meter measures electrical conductivity. Dissolved minerals and salts carry an electric charge, so the more of them present, the better the water conducts — and the meter converts that into an estimated ppm value.
Dissolved ions — calcium, sodium, magnesium, chloride — gather at the probe tips. The meter reads how easily an electric current passes between them, then converts that into ppm.
1
Dissolved ions carry charge
Minerals and salts in the water conduct electricity.
2
The probe measures conductivity
Read in microsiemens per centimetre (µS/cm).
3
It converts to an estimated TDS
A value in ppm — on screen within a couple of seconds.
The lab reference: APHA 2540 C
The gold-standard lab method is different: gravimetric analysis, where a sample is evaporated and the leftover residue is weighed directly. It’s more precise, but impractical for daily use. A conductivity meter trades a little precision for something you can use at home, every day, on any tap.
04 · Backed by research — the WHO scale
Not a safety cutoff — a taste-panel rating, precisely defined.
The number people usually reach for — “up to 900 is drinkable” — is a rough gloss on something more specific. The World Health Organization’s background document on TDS reports a five-tier palatability scale, built from taster-panel ratings, not a toxicity threshold.
| mg/L (ppm) | Taste-panel rating | What the WHO document reports |
|---|---|---|
| Below 300 | Excellent | Rated “excellent” by taste panels — the range most independent guides also recommend for daily drinking, often narrowed to 100–300 mg/L for the best balance of taste and mineral content. |
| 300–600 | Good | Rated “good” — a noticeable mineral presence, still pleasant to most tasters. |
| 600–900 | Fair | Rated “fair” — taste starts to decline; a reasonable point to check where your water is coming from. |
| 900–1200 | Poor | Rated “poor.” For context, the EPA’s own non-enforceable secondary guideline sits far lower — at 500 mg/L — based on taste and staining. |
| Above 1200 | Unacceptable | Rated “unacceptable” by taste panels on grounds of palatability. |
Source: World Health Organization, Total Dissolved Solids in Drinking-water (background document, WHO/SDE/WSH/03.04/16).
05 · Backed by research — the two extremes
When TDS runs too low — or too high.
◇ Too low
Very low-mineral water isn’t automatically the purest choice.
Water stripped of nearly all its minerals — through reverse osmosis, distillation, or desalination — removes contaminants, but it also removes the calcium, magnesium, and (in desalinated seawater) iodine that drinking water naturally contributes to the diet.
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Diuresis and hormone changes
Very low-TDS or distilled water intake is associated with increased diuresis, altered sodium/chloride balance, and changes in T3 and cortisol secretion in controlled research.
WHO background document, citing Rakhmanin et al.🪨
Magnesium and calcium deficiency
Low-TDS water is linked to magnesium and calcium deficiency; goitre is among the health effects reported in the reviewed literature.
Health risk from drinking demineralized water🌊
Iodine removed by desalination
Desalinated water — which removes naturally occurring iodine — has raised concern in populations with pre-existing iodine deficiency, including children and pregnant women.
Koren et al. (2018), J. Water & Health⚖
The counter-finding, in the same country
A large population-based follow-up found no significant increase in hypothyroidism among heavy consumers of desalinated water.
Same study, Tel Aviv University follow-upThe honest version
Mineral-deficient water is a real, researched contributor to magnesium, calcium, and iodine shortfall — and those minerals matter. That’s different from claiming low TDS alone causes thyroid disease; iodine from salt and diet remains the dominant factor.
△ Too high
High readings aren’t automatically dangerous — but they’re worth investigating.
TDS measures quantity, not identity. A high reading can mean your water is naturally rich in harmless calcium and magnesium — “hard water” — or it can mean nitrates, fluoride, or heavy metals are present. The number alone can’t tell the difference.
Commonly reported at high TDS
- Scale buildup in pipes, kettles, and appliances
- Salty, bitter, or metallic taste
- Staining on fixtures
- Reduced palatability, which can discourage adequate hydration
What a TDS number can’t tell you
- Whether high readings come from harmless minerals or specific contaminants
- The presence of bacteria or pathogens
- The identity of individual dissolved substances — that needs targeted lab testing
No universal safe/unsafe line
There is no single universal TDS level that defines all water as safe or unsafe. TDS measures the total amount of dissolved substances, not their identity — consistent with WHO and EPA guidance on TDS as a screening, not diagnostic, measurement.
06 · The sweet spot
Most independent guides land in the same narrow band.
Strip away the marketing language across water-quality sources, and a consistent range shows up again and again for everyday drinking water.
50–150 ppmtaste floor — often cited as the point below which water starts to taste flat, having lost most of its minerals
100–300 ppmthe range most consistently recommended for daily drinking — balancing taste and mineral content
>500 ppmthe EPA’s non-enforceable secondary guideline, based on taste and scaling — not toxicity
Read the taste-panel language and the EPA’s secondary standard together, and the picture converges: a middle band — roughly 100 to 300 ppm — is where everyday drinking water sits most comfortably. It isn’t a fringe number. A TDS meter is simply what lets you find out which side of that band your own water — tap, filtered, RO, or bottled — actually falls on.
07 · Why choose Tattwas
A precise reading, honest about its limits.
A compact digital pen that reads the TDS of any water sample in seconds — tap, RO, filtered, or bottled — with no calibration ritual for everyday use.
| Tattwas TDS Meter | Paper / strip tests | Lab gravimetric test | |
|---|---|---|---|
| Reading type | Digital ppm value on screen | Rough colour match | Exact, by weight |
| Tracking over time | Easy — consistent readings | Inconsistent per strip | Costly to repeat |
| Speed | Under 10 seconds | Minutes | Days (send-away) |
| Reusable | Yes | Single-use | — |
| Everyday calibration | None required | — | Lab-controlled |
| Identifies contaminants | No — screening only | No | Yes — definitive |
| Cost per use | Negligible | Recurring | High |
| Warranty | 6 months | None | — |
What honesty looks like on a spec sheet
This device is a water-quality screening tool, not a certified safety-testing instrument. For a full contaminant profile — bacteria, specific heavy metals, pesticide residues — use a certified water-testing laboratory. Saying so plainly is the point.
08 · How to use
Four steps. Ten seconds. No guesswork.
1
Uncap and power on
Remove the protective cap and switch the meter on. The display wakes and is ready to read.
2
Submerge to the line
Dip the probe into the water up to the marked line — no further. Submerging past it can let water reach the body.
3
Stir and let it settle
Stir gently and wait a few seconds for the reading to stabilise. Press HOLD to freeze the value if you want to note it down.
4
Read, then rinse
Note the ppm value. Rinse the probe with clean water, dry it, and re-cap before storing.
Good practice
- Test the same source at different times to catch seasonal or supply changes.
- Compare tap, filtered, and RO output side by side to see what your filtration is actually doing.
- Keep the probe dry and capped between uses to protect the sensor.
10 · Frequently asked
The questions we get before the first reading.
How accurate is a TDS pen versus a lab test?
It estimates TDS from electrical conductivity — excellent for tracking and screening your water over time. It isn’t a certified contaminant analysis; to identify specific substances, use a lab.
What TDS level should I aim for?
Roughly 100–300 ppm balances taste and minerals; below about 50 can taste flat; the EPA’s aesthetic guideline is 500. It’s a taste and aesthetic guide, not a strict safety line.
Can it detect bacteria or heavy metals?
No. TDS measures the total quantity dissolved, not its identity. It cannot detect pathogens or name specific metals — that requires targeted laboratory testing.
What powers it, and how long does it last?
A replaceable button cell, with a long standby life suited to occasional daily use. There’s no charging cable — pick it up, take the reading, cap it, and put it away.
Do I need to calibrate it?
No calibration ritual is needed for everyday use. Just keep the probe clean and capped. Advanced users can recalibrate against a known-value solution if they wish.
Is low-TDS RO water bad for me?
Not inherently — but very low-mineral water removes calcium and magnesium (and iodine in desalinated water). Diet still dominates mineral intake; the meter shows if your RO is over-stripping.
How do I clean and store it?
Rinse the probe with clean water after each use, dry it, and keep it capped. Storing it dry and covered protects the sensor and keeps readings consistent.
Can I use it beyond drinking water?
Yes. It reads TDS in any water sample, so it’s handy for aquariums, hydroponics and gardening, and for checking whether an RO cartridge still needs replacing.
11 · References & sources
Scientific evidence.
Every claim in this dossier traces back to a source. The standards and studies below anchor the thresholds and the trade-offs.
WHO & regulatory standards
1Total Dissolved Solids in Drinking-water
World Health Organization. Background document for WHO Guidelines for Drinking-water Quality (WHO/SDE/WSH/03.04/16). who.int
2Secondary Drinking Water Standards
US EPA. Non-enforceable guideline of 500 mg/L for TDS, based on aesthetic effects. epa.gov
3Bureau of Indian Standards (BIS) 10500
Acceptable and permissible TDS limits for drinking water in India.
Low-TDS / demineralized water
4Health Risk from Drinking Demineralized Water
Review summarising findings on distilled / low-TDS water intake, including effects on T3, cortisol, and mineral balance (citing Rakhmanin et al.).
5Adverse health effects of demineralized water
WHO commissioned study, A.N. Sysin Institute of General and Public Hygiene — magnesium and calcium deficiency.
Desalination & iodine
6Sea water desalination and removal of iodine: effect on thyroid function
Koren G, Amitai Y, Shlezinger M, et al. (2018). Journal of Water and Health, 16(3):472–475.· Read source →
Measurement method
7Standard Method 2540 C
American Public Health Association (APHA) — gravimetric total dissolved solids, the reference laboratory method.
Product
8Manufacturer specifications
Digital TDS meter, button-cell powered, 6-month brand warranty.
A note on scope. This device is intended for general water-quality screening and is not a certified safety-testing instrument. If you have specific health concerns related to your water supply, consult a certified water-testing laboratory or your physician.
Water has a number. Now you can read it.
A screening signal you can take on any tap, filter, RO unit, or bottle — with the thresholds traced back to the WHO taste-panel scale and the EPA’s secondary standard, and the limits stated plainly.
Order Your Tattwas TDS MeterThe Tattwas Digital TDS Meter is a water-quality screening tool, not a certified safety-testing instrument or a medical device. It cannot detect bacteria, pathogens, or specific heavy metals. For a full contaminant profile, use a certified water-testing laboratory; for health concerns related to your water supply, consult your physician.