Decrypting the Number on Your Faucet: What Is TDS and How Does It Relate to Your Drinking Water?

Imagine this: you’ve just moved into a new home or finished a kitchen renovation. You turn on your sleek, new faucet for the first time, and a small LED screen on its base lights up, displaying a number: 287. You watch as the water flows, and the number fluctuates slightly. What is this? A water temperature gauge? A pressure reading?

This little number, a feature on increasingly common “smart faucets” like those paired with modern filtration systems, is your real-time Total Dissolved Solids (TDS) reading. And for most people, it raises more questions than it answers. Is 287 good? Is it bad? Should I be worried?

If you’ve ever felt this flicker of confusion, you’re in the right place. Let’s demystify this number together. We’re going to skip the dense chemistry jargon and figure out what TDS actually means for you and your family’s drinking water.

What in the World Are Total Dissolved Solids? The Soup Analogy.

The easiest way to understand TDS is to think of a glass of water as a bowl of clear soup broth.

Even though the broth looks perfectly clear, you know it contains things you can’t see—salt, spices, and flavorings that have completely dissolved into the water. Total Dissolved Solids are simply the sum total of all these dissolved “things” in your water.

These “things” are mostly inorganic salts like calcium, magnesium, and sodium, along with a small amount of organic matter. They found their way into your water as it traveled through rock and soil to get to your local treatment plant. Essentially, TDS is a measure of the total quantity of dissolved substances in your water, typically measured in parts per million (ppm), which is the same as milligrams per liter (mg/L). So a TDS reading of 287 ppm means that in every liter of your water, there are 287 milligrams of dissolved stuff.

The Million-Dollar Question: Is a High or Low Number Better?

This is where things get interesting, and where most of the confusion lies. Our brains are wired to think in simple terms: high number = bad, low number = good. But with TDS, it’s not that simple.

Let’s bust a huge myth right now: TDS is not a measure of pollution. A high TDS reading does not automatically mean your water is dirty or unsafe. Likewise, a low TDS reading doesn’t guarantee it’s perfectly pure.

To understand why, let’s look at two common misconceptions.

Myth #1: High TDS is Always Bad. (The Mineral Water Twist)

Have you ever paid a premium for a bottle of fancy mineral water, like Evian or Fiji? If you were to measure its TDS, you might be shocked. Evian, sourced from the French Alps, can have a TDS of around 300 ppm. Many other mineral waters have even higher levels.

Why? Because they are rich in naturally occurring minerals like calcium and magnesium, which are… you guessed it, dissolved solids! In this case, a high TDS is a sign of the very mineral content that people pay extra for. The World Health Organization (WHO) notes that TDS levels primarily affect the taste of water. Water with a very low TDS (under 100 ppm) can taste “flat,” while water with a TDS over 500 ppm (the EPA’s non-enforceable secondary standard) may have a noticeable salty or bitter taste.

So, a high TDS reading in your tap water could simply mean you have “hard water,” rich in harmless minerals. It’s not inherently dangerous.

Myth #2: Low TDS is Always Safe. (The Invisible Villains)

This is the more critical myth to bust. TDS meters work by measuring the electrical conductivity of water. Dissolved salts are great conductors of electricity. However, many of the most dangerous contaminants are not.

Nasty things like lead from old pipes, pesticides from agricultural runoff, and certain pharmaceuticals are incredibly harmful even in microscopic amounts. But because they don’t conduct electricity well and exist in such tiny quantities, they contribute very little to the overall TDS reading.

You could have water with a “good” TDS reading of 150 ppm that still contains unsafe levels of lead. The TDS meter is completely blind to these specific threats. It’s like trying to judge the safety of a neighborhood by only counting the total number of people on the street, without knowing if any of them are dangerous.

Your Actionable Guide: How to Think About Your Home’s TDS

So, if TDS isn’t a direct measure of safety, what’s the point of that number on your faucet? It’s a useful indicator, but you have to be the smart interpreter. Here’s a simple framework:

1. Use it as a Baseline. When you first measure your tap water’s TDS, that’s your starting point. Let’s say it’s 300 ppm. This number tells you about the general mineral content and taste profile of your municipal water.
2. It’s a Great Tool for Checking Your Filter’s Performance. This is the primary job of a TDS meter on a filtration system. If your tap water is 300 ppm, and after running it through a system like a Reverse Osmosis (RO) unit, the faucet shows a TDS of 20 ppm, you have a clear, quantitative sign that the filter is doing its job of removing a massive percentage (in this case, 93%) of dissolved solids. If, six months later, that number creeps up to 100 ppm, it’s a data-driven signal that your filter might need maintenance.
3. Don’t Rely on it for Safety. For peace of mind about specific contaminants like lead, chlorine, or cysts, TDS is the wrong tool. The only way to know for sure is to look for technology and products that are independently certified by organizations like NSF International to remove those specific threats (e.g., certification to NSF/ANSI 58 for lead reduction).

So, What If I Want a Lower Number?

If your water has a high TDS and you dislike the taste, or if you simply want the peace of mind of drinking highly purified water, you might consider technology designed to reduce it.

The most effective method for drastically reducing TDS is Reverse Osmosis (RO). This technology uses a very fine membrane to physically block and separate almost all dissolved solids from water molecules. A modern, efficient RO system can take water with a TDS of 300 ppm and purify it down to 20 ppm or even lower, which is why they are often equipped with TDS meters to showcase their powerful performance.

But now, when you see that low number on the faucet, you’ll understand exactly what it represents: not just a number, but a reflection of a process that has removed the vast majority of dissolved “things”—from harmless minerals to potentially other substances—from your water. You’ve decrypted the code.