Playing with a cheap water quality TDS meter

[Mikedefieslife]

Recently been playing with one of those Chinese water quality meters as i'm planning on changing the old flexible water hoses to plastic speedfit or similar.

I was surprised to find that water from my sing tap that had been sitting for a week had a TDS reading of around 350.

Oddly, water from the same source but run through my General Ecology filter that even filters out viruses was over 360. The actual figures aren't too important as such a cheap tester is going to have a margin of error, but multiple tests have shown the unfiltered water to constantly outperform the filtered. Odd.

A fresh bottle of mineral water was used a control. It measured closer to 240.

 

[AntarcticPilot]

Recently been playing with one of those Chinese water quality meters as i'm planning on changing the old flexible water hoses to plastic speedfit or similar.

I was surprised to find that water from my sing tap that had been sitting for a week had a TDS reading of around 350.

Oddly, water from the same source but run through my General Ecology filter that even filters out viruses was over 360. The actual figures aren't too important as such a cheap tester is going to have a margin of error, but multiple tests have shown the unfiltered water to constantly outperform the filtered. Odd.

A fresh bottle of mineral water was used a control. It measured closer to 240.

The D stands for "dissolved".. No filter will remove stuff that is dissolved in the water; only particulate matter. Mineral water has a high TDS (it's MINERAL water). It's quite possible that your filter actually addds a small amount of dissolved material. I suggest you check it against distilled water - the stuff from a tumble dryer ought to have quite a low TDS.

 

[VicS]

Recently been playing with one of those Chinese water quality meters as i'm planning on changing the old flexible water hoses to plastic speedfit or similar.

I was surprised to find that water from my sing tap that had been sitting for a week had a TDS reading of around 350.

Oddly, water from the same source but run through my General Ecology filter that even filters out viruses was over 360. The actual figures aren't too important as such a cheap tester is going to have a margin of error, but multiple tests have shown the unfiltered water to constantly outperform the filtered. Odd.

A fresh bottle of mineral water was used a control. It measured closer to 240.

I guess your meter just measures the electrical conductivity and displays the reading as an approximate value for the total dissolved solids.

As Antarctic pilot says ordinary filters , and carbon filters will not remove dissolved solids.

You will find quite a wide range of values for different bottled waters and for tap water from different areas.

Brita filters do I believe remove some / most ?? of the dissolved solids by ion exchange but I have never actually tested the water from one although I have one. No doubt there are others that do so as well.

Any reading you get for distilled or de-ionised water will be due to dissolved carbon dioxide .

 

[thinwater]

Calling a TDS meter a "water quality" meter is a stretch that is nearly fraudulent, for the reasons others have mentioned.

The only applications where TDS alone is meaning full are RO water makers and battery/engine coolant make-up water.
* Water maker. The manufacture will give a range of specs.
* Battery or engine coolant. The result should be VERY low, preferably below 50 ppm.
The only useful control is distilled water, which should read less than 10 ppm. Bottle mineral water can be quite high, and that is NOT a bad thing... except for batteries (never use bottled drinking water in a battery).

In fact, there is scholarly information available (and WHO and EPA) that suggests that water high in minerals, specifically Caand MG, is good for you, with no apparent upper limit.

As for drinking water quality, this post should give some good starting information:
http://sail-delmarva.blogspot.com/2014/06/drinking-water-filtration-short-version.html

This discusses potential problems with low-mineral drinking water. This is not my soap box, just some interesting information I've come across. If nothing else, it makes it clear that TDS (other than water makers) is no measure of water quality.
http://sail-delmarva.blogspot.com/2014/05/ro-water-what-are-we-missing.html

 

[pvb]

I use a TDS meter to check the quality of the water coming out of my resin filter (used for car rinsing, window cleaning, etc). My regular tap water is around 350-400ppm; the water coming out of the filter is typically 5ppm.

 

[thinwater]

I use a TDS meter to check the quality of the water coming out of my resin filter (used for car rinsing, window cleaning, etc). My regular tap water is around 350-400ppm; the water coming out of the filter is typically 5ppm.

Tell us a little more about the resin system. I'm curious.

 

[pvb]

Tell us a little more about the resin system. I'm curious.

Basically, it's a means of removing impurities from water by passing it through a filter bed of resin beads, which are composed of organic polymer chains that have charged functional groups. The water coming out is close to 0ppm TDS, and will evaporate without leaving little white marks. That's why resin filters are used by window cleaners - and by anally-retentive car washers! I use a Raceglaze filter ( http://www.raceglaze.co.uk/race-glaze/400-litre-0ppm-car-washing-filter/ ) with a hosepipe and trigger jet, and only use it for rinsing each panel of the car after washing it, so very little filtered water is used in a typical wash session. It dries perfectly, no need to use microfibre towels, even in strong sunlight.

 

[VicS]

Tell us a little more about the resin system. I'm curious.

Ion exchange

 

[alant]

Basically, it's a means of removing impurities from water by passing it through a filter bed of resin beads, which are composed of organic polymer chains that have charged functional groups. The water coming out is close to 0ppm TDS, and will evaporate without leaving little white marks. That's why resin filters are used by window cleaners - and by anally-retentive car washers! I use a Raceglaze filter ( http://www.raceglaze.co.uk/race-glaze/400-litre-0ppm-car-washing-filter/ ) with a hosepipe and trigger jet, and only use it for rinsing each panel of the car after washing it, so very little filtered water is used in a typical wash session. It dries perfectly, no need to use microfibre towels, even in strong sunlight.

The water used by windowcleaners, is RO water, which is somewhat more sophisticated.
A resin ion exchange bed, will only do what it says on the tin, exchange the ions in the incoming water, for something else. Typically the resin will hold Na ions & exchange rhat sodium for Ca & Mg ions, which are left behind on the resin. There will be no change in discernable TDS.

 

[pvb]

The water used by windowcleaners, is RO water, which is somewhat more sophisticated.

Some use RO, some use DI.

A resin ion exchange bed, will only do what it says on the tin, exchange the ions in the incoming water, for something else. Typically the resin will hold Na ions & exchange rhat sodium for Ca & Mg ions, which are left behind on the resin. There will be no change in discernable TDS.

I'm happy to invite you along to use my TDS meter on my tapwater, and then on the output from my resin filter, and then eat your words.

 

[thinwater]

Basically, it's a means of removing impurities from water by passing it through a filter bed of resin beads, which are composed of organic polymer chains that have charged functional groups. The water coming out is close to 0ppm TDS, and will evaporate without leaving little white marks. That's why resin filters are used by window cleaners - and by anally-retentive car washers! I use a Raceglaze filter ( http://www.raceglaze.co.uk/race-glaze/400-litre-0ppm-car-washing-filter/ ) with a hosepipe and trigger jet, and only use it for rinsing each panel of the car after washing it, so very little filtered water is used in a typical wash session. It dries perfectly, no need to use microfibre towels, even in strong sunlight.

Thanks!

Actually, I'm a chemical engineer with 40 years experience, including some very large DI work. I was curious about how you used it an what specific equipment was working for you. Thank you for that. I can see that the volume would be quite low if only for the last rinse.

The problem with RO for a little dock-side unit is flow rate and pressure. Sure, you could use a household unit, but you'd need a reservoir and a pump or some other manner of complication. A resin bed avoids all that.

Yes, a mixed bed can remove ALL of the ions, not just exchange them. RO is generally cheaper for larger volumes and higher concentrations, DI beds for lower volumes and very fine polishing; labs often do both.

 

[VicS]

Start again!

The water used by windowcleaners, is RO water, which is somewhat more sophisticated.
A resin ion exchange bed, will only do what it says on the tin, exchange the ions in the incoming water, for something else. Typically the resin will hold Na ions & exchange rhat sodium for Ca & Mg ions, which are left behind on the resin. There will be no change in discernable TDS.

What you are describing is softening by a process often called base exchange.

All the dissolved solids can be removed by deionisation, in outline as follows.

First the water is passed through a cation exchange resin bed in the hydrogen (acid) form. All the cations( Ca, Mg, Na, K etc) are removed and replaced by H ions .

The water is then passed through an anion exchange resin bed in the hydroxyl ( OH) form. All the anions are removed and replaced by OH ions.

H + OH = water !

As an intermediate stage CO₂ can be scrubbed out giving cost effective way of removing carbonate and bicarbonate ions.

The final stage is to pass the water through a bed of mixed cation and anion exchange resins to remove what remains from the previous stages.

All the resins can be regenerated. The cation resin with a dilute strong acid and the anion resin with sodium hydroxide solution

 

[alant]

Some use RO, some use DI.



I'm happy to invite you along to use my TDS meter on my tapwater, and then on the output from my resin filter, and then eat your words.

There are mixed bed ion exchange systems, but conventionaly used to 'polish' out any dissolved solids, after a previous process to reduce tds. Using such a unit on high tds tapwater, wouldn't take long to effectively kill it. Recharging the anion/cation resin mix is extremely difficult, they are usually done as seperate units.
What do you use to recharge the resin?

 

[pvb]

There are mixed bed ion exchange systems, but conventionaly used to 'polish' out any dissolved solids, after a previous process to reduce tds. Using such a unit on high tds tapwater, wouldn't take long to effectively kill it. Recharging the anion/cation resin mix is extremely difficult, they are usually done as seperate units.
What do you use to recharge the resin?

New resin.

 

[alant]

Start again!



What you are describing is softening by a process often called base exchange.

All the dissolved solids can be removed by deionisation, in outline as follows.

First the water is passed through a cation exchange resin bed in the hydrogen (acid) form. All the cations( Ca, Mg, Na, K etc) are removed and replaced by H ions .

The water is then passed through an anion exchange resin bed in the hydroxyl ( OH) form. All the anions are removed and replaced by OH ions.

H + OH = water !

As an intermediate stage CO₂ can be scrubbed out giving cost effective way of removing carbonate and bicarbonate ions.

The final stage is to pass the water through a bed of mixed cation and anion exchange resins to remove what remains from the previous stages.

All the resins can be regenerated. The cation resin with a dilute strong acid and the anion resin with sodium hydroxide solution

Softening is only anion exchange resin, used to exchange Ca, Mg, for Na, with the outgoing water containing sodium carbonate/sulphate, which remain in solution when heated.
Cation exchange will not remove these anions, I think you have your +/- the wrong way around.

 

[VicS]

Softening is only anion exchange resin, used to exchange Ca, Mg, for Na, with the outgoing water containing sodium carbonate/sulphate, which remain in solution when heated.
Cation exchange will not remove these anions, I think you have your +/- the wrong way around.

As I understand it,

A cation exchange resin in the sodium form is used for water softening. It exchanges the Ca²⁺ and Mg²⁺ cations for Na⁺ .

Anions eg HCO₃^-, SO₄^2-, Cl^- are not affected by a cation exchange resin

 

[alant]

As I understand it,

A cation exchange resin in the sodium form is used for water softening. It exchanges the Ca²⁺ and Mg²⁺ cations for Na⁺ .

Anions eg HCO₃^-, SO₄^2-, Cl^- are not affected by a cation exchange resin

I'm getting confused myself now.

 

[pvb]

I'm getting confused myself now.

"getting" ?

 

[VicS]

I'm getting confused myself now.

You are only confused because you seem to believe that the positively charged ions ( calcium , magnesium, sodium etc) are called anions and that the negatively charged ions ( carbonate, bicarbonate, sulfate etc) are called cations.

The opposite is the case because they are named according to the electrode ( of a galvanic cell ??) to which they are attracted. The positively charged ions are attracted to the negative electrode , or cathode, and are therefore called cations. The negatively charged ions ions are attracted to the positive electrode, or anode, and are therefore called anions.
I believe we have Faraday to thank for the nomenclature

 

[alant]

"getting" ?