​What does TDS in water mean?

By Bob Fear

​What does TDS in water mean?

What’s the meaning of TDS in drinking water and is it a good measure of quality? We take a look at what constitutes TDS in water and examine all the facts around the different levels of TDS in water. What’s a good TDS level and what’s a bad TDS level?

TDS stands for total dissolved solids and is a measure of all the dissolved organic and inorganic substances in drinking water. On the face of it, it seems like a good measure of the quality of our drinking water as we’d expect to not want lots of dissolved contaminants in our water. But the truth isn’t so straightforward as some dissolved substances in drinking water occur very naturally and are good for our health. Therefore, TDS as a measure of the quality of our drinking water may be misleading.

TDS levels can be misleading

‘TDS is relatively easy to measure with an inexpensive meter. Because of its availability and ease of use, the TDS meter can be used as a misleading marketing tool by the reverse osmosis technology industry to convince consumers that their water may be causing harm,’ concludes Dr Danielson. ‘However, let’s be clear, the mere presence of TDS does not indicate unhealthy drinking water.’

Richard E. Danielson, PhD is author of over sixty publications, reports and presentations on water quality and environmental and public health microbiology

What are good and bad TDS levels?

In 2003, The World Health Organisation (WHO) convened a panel of taste testers and decided on the following scale:

50 - 300 TDS = excellent

300 - 600 = good

600 - 900 = fair

900 - 1,200 = poor

1,200+ = unacceptable

This is all based on taste, smell and feel rather than health and safety, so it’s subjective. The other problem with measuring TDS in water is that it’s a blanket measurement. So we should take into account what’s actually being measured.

What are TDS made up of?

TDS are pretty much anything in water that isn’t the actual water itself - your basic H20. Water will try to absorb and dissolve anything it comes close to - that’s why it’s called a universal solvent. If it sits in a plastic bottle for long enough, that plastic, being slightly permeable, will begin to leach into the water. If you sit an open glass of water next to something with a strong smell, given the chance, the water will begin to smell the same.

Our drinking water will naturally pick up a fair few passengers along its way to our taps. For a start, historically our drinking water has always come from surface water (from rivers, lakes and reservoirs) or groundwater (from the cracks and spaces between porous underground rocks, soil and sand). Water from both of those sources will have picked up stuff like minerals, dirt, microplastics, pesticides and herbicides. Our local water treatment works will then add chlorine to kill the bacteria that grows in water. Even after that, our water may still pick up dirt and rust from the pipes leading to our properties. If any of these are present in your tap water, an easily available TDS meter will measure the amount there is.

Why is the TDS level not a good measure of the quality of water?

A TDS meter will indiscriminately measure the amount of other substances found in our tap water, no matter what they are. While no-one wants bacteria, dirt, rust, sand, metal, microplastics, pesticides, herbicides and chlorine in our drink, a whole load of naturally occurring minerals are a good thing. Bottle of mineral water, anyone? Yup, huge business has been found from bottling groundwater at source rich in minerals and selling it to health conscious consumers. Some companies even add minerals to the water to increase its health value. So having minerals such as calcium, magnesium and potassium in your drinking water is a good thing - and a TDS meter will pick these up.

We asked Richard E. Danielson PhD, Environmental and Public Health Microbiologist, for an independent view on TDS levels in water. Here’s what he said:

‘Humans require inorganic salts and minerals to maintain natural health. There are those in the water treatment industry who would label TDS in general as a detriment to water quality and human health. However, TDS, and especially magnesium and calcium, can contribute up to about 20% to the daily requirement of these available minerals.’

These are the TDS levels in bottled mineral water, and how the WHO would class their taste:

Perrier = 47 (The WHO would class this as tasting ‘flat’)
Fiji = 222 (WHO class = excellent)
Hildon = 312 (WHO class = good)
Evian = 357 (WHO class = good)
San Pellegrino = 1109 (WHO class = poor)

How to reduce TDS in water

‘There are other constituents (in TDS, besides natural minerals) of immediate concern… such as chlorine, pesticides, heavy metals, microorganisms, and pharmaceuticals,’ says Dr Danielson.

A water filter will reduce the TDS level in drinking water. An active carbon filter will remove chemicals, including the chlorine added by the water treatment works, along with substances including copper and lead. Along with an activated carbon filter, the Virgin Pure system has additional filters which will also reduce dirt, microplastics, rust, sand and sediment. It also contains an ultraviolet light which kills off bacteria and stops it growing once the disinfecting chlorine has been removed.

While a reverse osmosis system will remove everything from your tap water, including the healthy minerals, the Virgin Pure filtration system leaves in all the naturally occurring minerals such as calcium, magnesium and potassium. All of which are good for our health. We even have a pre-filter which prevents the calcium and magnesium from bonding and creating scale.

Therefore, the TDS level in Virgin Pure water will include those healthy minerals, the same as it would in shop-bought mineral water.


United States Department of Agriculture - Vitamins and Minerals: https://www.nal.usda.gov/legacy/fnic/vitamins-and...

Water Quality Association - Consumption of Low TDS Water, 2013

World Health Organization - Total Dissolved Solids in Drinking Water, WHO/SDE/WSH/03.04.16. 2003

World Health Organization, EU Water Framework, EPA

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