How to use a TDS meter?

We all know what TDS stands for. No, it’s not Tax Deducted at Source. When it comes to water purification, TDS stands for Total Dissolved Solids. 

TDS tells you how much dissolved solids are there in your water but not what is there. Even if there are naturally occurring minerals in your water, your TDS meter will still read some number. 

So, if your water has a TDS of 300 ppm, it does not necessarily mean it’s highly polluted or the water is impure. That doesn’t mean water with a TDS of 100 ppm is completely healthy. It could be devoid of essential minerals like calcium and magnesium. 

This guide will help you understand how you can measure TDS, how to use a TDS meter and what you can do to purify your water. 

What is a TDS meter?

A TDS meter is a small handheld device which measures the amount of dissolved solids in your water. You dip the meter in a glass of water and a number appears on the end of the meter which shows a number. This is measured in parts per million (ppm). 

To understand this better, think of the TDS meter as a thermometer. When you use a thermometer on a person, it measures the temperature of the body and tells you if the person has a fever or not. It doesn’t diagnose why or how the person has a fever. This is very similar to how a TDS meter measures the dissolved solids in your water. 

How does a TDS meter work?

Dissolved salts and minerals carry a tiny electrical charge, so the more of them in your water, the better it conducts electricity. The two metal probes at the tip of the meter pass a small current through the water and measure how easily it flows. The meter then converts that conductivity into a TDS number in ppm.

Here’s the catch. The meter doesn’t actually see what’s in your water. It only reads conductivity and does the maths. That’s why it can tell you how much is dissolved, but not what is dissolved.

Types of TDS meters

Not all TDS meters look alike. Here are the ones you’re most likely to come across.

Handheld pen meters: These are the most common and the most affordable. They’re slim, run on small batteries and fit in a drawer. If you only want to check your water once in a while, this is the one to pick.

Meters with a temperature display: Conductivity changes with temperature, so these meters show the water temperature along with the TDS reading. Some also adjust the reading for temperature automatically, which makes the result a little more reliable.

Built-in or inline meters: Some water purifiers come with a TDS meter fitted into the system, which shows the reading without you having to dip anything. It’s convenient, but it usually reads only the water in that particular line, so a handheld meter is still handy for checking your tap water.

What do you need before you start?

Did you imagine wearing a lab coat and walking into a chemistry lab to measure the TDS of your water? It’s not a difficult process. Just gather these.

• A clean glass: Use a glass or a steel tumbler that has been rinsed well. Leftover soap or old water can throw off your reading.
• Fresh batteries: Weak batteries can give you odd or fluctuating numbers. If your meter has been lying around for months, check it first.
• Your water sample: Fill the glass with enough water to cover the probe up to the marked line. Room-temperature water gives the most reliable result, so avoid hot or ice-cold samples.

How to use a TDS meter: step by step

1. Take off the cap. Remove the protective cap so the probes are exposed.
2. Switch it on. Press the power button. The screen should show zero or a blank reading.
3. Dip the meter into the water. Place the probe end into the glass. Don’t go beyond the maximum immersion line marked on the meter, because the electronics at the top are not waterproof.
4. Stir gently. Give it a light swirl to get rid of air bubbles stuck to the probes. These can cause incorrect readings.
5. Wait for the number to settle. The reading will flicker for a few seconds. Wait until it stops changing.
6. Note the reading. Some meters have a “hold” button that freezes the number so you can lift the meter out and read it. If yours doesn’t, read it while it’s in the water.
7. Rinse and dry. Wash the probes with clean water, shake off the extra water, dry them and put the cap back on.

A small tip: Always rinse the probes with the water you’re about to test before you start. This way, the earlier sample doesn’t change your result.

How to read your TDS meter result? 

You have a number. What does it mean? Here’s a quick guide. 

Remember what we covered in our guide on the full form of TDS: there is no one magic number. A high reading doesn’t automatically mean the water is harmful, and a low reading doesn’t automatically mean it’s safe. Think of the number as the first clue, not the final verdict. (If you’d like to know more, read our TDS full form blog on safe TDS levels.)

Test tap water vs. purified water

Here’s a simple trick. Test your tap water first. Then test the water that comes out of your purifier. Compare the two numbers.

If you have an RO purifier: The purified water should show a clearly lower TDS than your tap water. If the two numbers are almost the same, your RO membrane may not be working properly, and it’s time to get it checked.

If you have a UV or UF purifier: Don’t be surprised if both readings are nearly the same. UV and UF purifiers neutralise bacteria and viruses but don’t remove dissolved solids. A similar TDS reading is normal here, and it doesn’t mean the purifier is faulty.

If the purified water reads very low: An RO purifier strips the water of minerals, so the reading can be quite low. This is why a mineraliser cartridge adds calcium and magnesium back to the water. A reading that rises slightly after the mineraliser stage is a good sign.

What a TDS meter can’t tell you?

A TDS meter is useful, but it has its limits. It cannot detect:

• Bacteria and viruses: These are living organisms and don’t change the conductivity of your water in a meaningful way. Water with low TDS can still carry them.
• Arsenic and fluoride: These can be dangerous in higher amounts, and a TDS meter can’t tell you whether they’re present.
• Pesticides and other chemicals: Organic contaminants like pesticides and fertiliser run-off won’t show up on a TDS meter.

So if you’re unsure about your water source, or you live in an area with known contamination, get your water tested in a lab. A TDS meter is a good quick check. A lab test is the complete picture.

What to do if your TDS is high or very low?

If your TDS is high (above 500 ppm): Use an RO purifier. RO (Reverse Osmosis) pushes water through a membrane under high pressure and leaves the dissolved solids behind. Boiling, candle filters and activated carbon don’t reduce TDS, so don’t rely on them here.

If your TDS is very low: Water with a very low TDS can taste flat and has fewer minerals. This is common after RO purification. The fix is a mineraliser, which adds calcium and magnesium back so your water is both pure and good for you.

How DrinkPrime helps?

Whether your TDS reading is high, low or somewhere in between, DrinkPrime has a purifier made for your city’s water. The range includes Copper, Alkaline, Mineral+, UV and Under-The-Sink purifiers. Since 100% RO strips the water of essential minerals, a mineral cartridge adds calcium and magnesium back to the RO-treated water.

DrinkPrime’s purifiers come on a rental basis. The monthly subscription starts at ₹349/month, with a refundable security deposit of ₹1,500. (Only the Under-The-Sink model has a security deposit of ₹1,999.) The rental covers the product, installation, delivery, maintenance and relocation. All recharges can be made on the app, which also helps you track your filter’s health and total water usage.

So grab a TDS meter, test your water, and if the number worries you, DrinkPrime takes care of the rest.

Frequently Asked Questions

1. How do I use a TDS meter?

Switch it on, dip the probe in a glass of clean water up to the marked line, stir gently, wait for the number to settle and note the reading.

2. Can I test hot water with a TDS meter?

It’s best not to. Temperature affects conductivity, so let the water come to room temperature for a more reliable reading.

3. What TDS reading is safe for drinking water?

A reading of 0-200 ppm is considered completely safe. Between 201 and 500 ppm, water is still acceptable as per BIS norms, but the taste might be affected.

4. Is a TDS meter accurate?

It’s accurate enough for a quick check, but it estimates TDS from conductivity and is not a lab result. It cannot detect bacteria, viruses or specific metals.

5. Why is my purified water’s TDS still high?

If you have an RO purifier, the membrane may need servicing. If you have a UV or UF purifier, it’s normal, because these don’t remove dissolved solids.

6. How often should I check my TDS?

When you move to a new home, when your water source changes, after the seasons change if you use borewell water, and after your purifier has been serviced.

7. Can a TDS meter tell me if my water is free of bacteria?

No. A TDS meter only measures dissolved solids. Bacteria and viruses need a purification method like UV or RO+UV, or a lab test.

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