What Is TDS in Water? Safe Levels, Testing & What High TDS Really Means

Every time you've looked at a water purifier, you've probably seen TDS in big bold letters. It's one of the most marketed — and least understood — terms in water purification. Let's fix that.

What TDS Actually Measures

TDS stands for Total Dissolved Solids. It's a measurement of all the inorganic salts and small amounts of organic matter that are dissolved in water. The unit is parts per million (ppm) or equivalently milligrams per litre (mg/L).

What contributes to TDS in your tap water?

• Calcium & magnesium — naturally dissolved from rocks; cause hardness
• Sodium & potassium — natural salts
• Bicarbonates, chlorides, sulphates — common dissolved ions
• Heavy metals — lead, arsenic, mercury (in trace amounts; the dangerous part)
• Nitrates & fluorides — from agriculture and natural sources
• Tiny dissolved organic compounds

TDS gives you a single number that summarises all of these together. It's not a perfect quality measure — a water sample at 200 ppm could be perfectly safe (all calcium & magnesium) or dangerous (heavy metals) — but it's a useful first signal.

BIS Safe Levels for Drinking Water

The Bureau of Indian Standards (BIS) IS 10500 sets the official Indian drinking water standard. Here's the practical chart, ranked from best to worst:

Indian Water by City (Typical TDS)

TDS varies enormously across India. Approximate municipal-water TDS values you'll see in most areas:

• Mumbai, Pune (lake-fed): 150–250 ppm
• Delhi, Gurgaon, Noida: 250–500 ppm
• Bengaluru, Chennai: 200–400 ppm
• Hyderabad: 250–600 ppm
• Jaipur, Ahmedabad, Lucknow: 400–800 ppm
• Rural / borewell water: 800–2500 ppm common

If you depend on a borewell or tanker supply, your TDS could be very different from the municipal average. That's why testing your specific source matters.

How to Test Your Water's TDS

A simple handheld digital TDS meter costs ₹250–500 on Amazon or Flipkart and gives an instant reading. The process:

1. Fill a clean glass with water directly from your usual tap (or RO outlet).
2. Switch on the TDS meter, dip the electrode 2–3 cm into the water.
3. Wait 5 seconds for the reading to stabilise.
4. Note the ppm number.

Test both your input water (raw tap) and your output water (after RO purification). The difference shows your RO membrane's effectiveness — it should reduce TDS by 85–95%.

What Does High TDS Mean for Health?

TDS itself isn't directly harmful — humans need some dissolved minerals for proper hydration. But high TDS in Indian water often correlates with:

• Hard water issues — scaling on appliances, dry skin, poor lathering
• Salty / metallic taste — unpleasant for drinking
• Hidden contaminants — fluoride, arsenic, nitrate often rise with TDS
• Long-term kidney stress from excess minerals

That's why TDS above 300 ppm is the typical threshold at which RO becomes essential.

Why Knite Purifiers Don't Strip TDS to Zero

Some old RO purifiers reduce TDS to under 30 ppm. That sounds great, but it's actually too pure — it tastes flat and lacks beneficial minerals. Modern purifiers like the Knite Prime use a TDS controller and a mineraliser to deliver output water at 80–150 ppm — clean, mineral-balanced, and great-tasting.

FAQs

What's the ideal TDS for drinking?

Between 50 and 300 ppm. Premium bottled water typically sits around 150–250 ppm.

Can low TDS (under 50 ppm) be harmful?

Not directly harmful, but the water tastes flat and lacks essential minerals like calcium and magnesium. Long-term consumption of demineralised water isn't recommended by WHO.

Does boiling water reduce TDS?

No. Boiling kills microorganisms but does nothing to dissolved salts. In fact, evaporation can concentrate TDS.

Why does my RO water show different TDS in summer vs monsoon?

Source water quality changes seasonally — monsoon dilutes TDS; summer can concentrate it. Test periodically.