Help me make a circuit to measure TDS/EC of Filtered Water

[SuzyC]

I just added a water filter for tap water. A friend said you can measure how well it works with a TDS meter which shows a reading in inverse ohms, but I don't have a TDS meter and would like to build one.

The TDS is best measured by evaporating water and measuring the mass of precipitated solid remaining.

I see TDS meters being sold that supposedly measure TDS by EC (electrical conduction).

My Questions to Expert WaterPurifiles:

1)What voltage level is required to accurately measure the EC of filtered water?
2)Is an AC current necessary?
3)Can a Fluke multimeter work using the ohms scale?
I have seen some water purifiers for chem lab that I think  use a NE2 neon bulb(2) 47K resistors and 120VAC. Is this correct?

[Kleinstein]

A normal filter should have very little effect on the electrical conductivity. This is because conductivity is determined by dissolved ions, but a mechanical filter normally on filters out particles and thus non dissolved parts.

It really help to measure conductivity with AC, as it reduces the effect of the electrodes and to reduce corrosion of the electrodes. With AC there is also a contact-less method to measure EC: it uses a kind of special ring core transformer that is emersed in the water. 

The voltage to measure EC can be rather low - something like 0.1-2 V AC and maybe a little more with DC because of errors from the electrodes. 

[Conrad Hoffman]

AFAIK, you want AC. I've done it with some 1 cm wide stainless steel shim electrodes on a 1 cm thick insulating block, making it easy to get ohms/cm. The voltage should be low enough that electrolysis doesn't complicate things too much. This was for DI water; tap water will be vastly more conductive, even with a filter.

[coppercone2]

the electrode geometry is important for getting readings that are meaningful and linear. You  can find equations online to make your probe, if you don't really care you can use a probe that is meant to measure water the presence of water and use a few calibration points.

To make a probe you would use a non resistive material with stainless rods of specific dimensions embedded into it, you would also want some kind of shield, its not that easy to make a accurate one.

If you use the equations available on the internet to dimension a probe, you will find that they are rather unreasonable if you use thin electrode rods. Like with 1mm rods it comes out to something like 6cm long to get good linearity between brine and ultra pure water, iirc. I also recall that basically the linearity sucks and you should have different probe geometries to cover different ranges to maintain linearity.

[ArthurDent]

There have been industrial meters available for a long time, like the one I have pictured below. Recently it seems everyone is making 'pen' type ones that are priced in the $10 up range. Water Filters Online and other distributors that sell whole systems have a couple of inline sensors with remote digital readout for $40-$50. I don't think it would be worth it to build a TDS meter unless you are really interesting in learning what works and what doesn't

[ArthurDent]

Here is some interesting information about TDS. I have not verified if this is totally correct but it is worth watching.

[SuzyC]

Thanks to all!

I am beginning to realize that EC/TDS meters do not detect the type or even the content of certain impurities. Resistance of the water doesn't show if organic toxins are a problem or whether the resistance measurement is low due to sodium, calcium, sulfates, potassium or iron, copper or magnesium or lead, hexavalent chromium, cadmium, arsenic or mercury!

It all started when my friend installed a $4000 6-stage RO water filter system and he boasts that it creates structured re-vitalized water that shows <30 micro-siemens of conductivity.

But that obviously doesn't tell the whole story.

I was already frightened. Every time they shut the water off in this 100+ yr old apt building plumbed with iron pipes we have a horror show. When the water is turned back on,  the water is mud, dark brown, with hard sediment. Water from the tap slowly sheds it brown color only after several hours. After a day or two, the water is crystal clear to the eye but does have a hard water's nasty taste. If boiled and poured into a glass jar, it will develop a cloudy-white precipitate at the bottom after a day in the fridge.

For the plumbers who do the work, this effect is a cash cow. The sediment clogs and fouls/damages every water valve, be it sink, shower, washing machine or toilet, creating a mountain of new business from tenants who soon complain of low faucet water volume or leaking water reservoir filling valves in the toilets.

If a glass filled with this water is emptied and allowed to dry, the water creates a hard to wash-off cloudy film on the drinking glass.

The water in this area is super hard, lots of calcium and GKW else.

Can drinking unfiltered water from my kitchen cold-water tap, even waiting several days after a repair event, be dangerous to drink?

Or is it a great source for minerals like calcium, zinc and iron in my diet?

The city says on their website that their water is safer than bottled water to drink! But that is before traveling through many pipes to finally get to be super-mineralized by the galv. iron plumbing of my apt building.

[ArthurDent]

Several years ago I personally installed a 4-stage 75 gallon RO filter system that cost under $180 at the time. My reasoning was I only wanted it for drinking water and the ice maker in the fridge so 75 gallon was more than enough. Dish and clothes washers and cooking is ok with the city water. I have been very pleases with the system and the RO filter element has lasted much longer than expected so I've only replaced it once but the other filters get replaced about once a year. I haven't felt the need for any testing.

[rstofer]

Short answer: Google for DIY TDS meter

Here is one example:
http://www.octiva.net/projects/ppm/

The crud floating in the water is suspended solids and can be removed with a particulate filter.  Micron pore size up to the user but the smaller the better as long as you can get sufficient flow and filter life.

Total DISSOLVED solids are, in fact, dissolved in the water and can not be removed with a particulate filter regardless of pore size.  That's what the RO process is used for.  It blocks dissolved solids and passes relatively pure water.  The flow rate will be low on small canister units and, for that reason, there is usually a storage tank between the filter and what are usually dedicated outlets.  We have one such outlet on each kitchen sink and one sink has a flash heater to warm it up.

At the outlet of an RO system you should have pretty good drinking water but there are a number of ionic contaminants that haven't been removed.  For these, you need ion exchange units and once you pass the water through the anion and cation resin beds you have deionized water suitable for manufacturing except for one last detail - some living organics will be left behind so you zap those with ultraviolet light.  This reduces the bacteria content before the water gets into the piping system.  The thing about these organics is that under high heat, they interact with the wafer and create carbide deposits which are a direct short circuit.  This is a huge factor in the yield of wafers.  Drinking DI water will pull minerals out of the body  -  the water is very aggressive.

https://en.wikipedia.org/wiki/Purified_water

Our well water is very low in incoming TDS - down in low 2 digits.  Surface water will be in the hundreds of PPM.

https://www.purewaterproducts.com/water-problems/total-dissolved-solids-tds

TDS is measured with conductivity

https://en.wikipedia.org/wiki/Total_dissolved_solids

I suppose water softening should be included:

https://en.wikipedia.org/wiki/Water_softening

Drinking soft water by folks with limitations on sodium might not be a good idea.  Our soft water goes to the showers and sinks.  That's why we have a separate system for drinking water.

[BrianHG]

I've been drinking and cooking with distilled water for 20 years now.  I call bullshit on it leaching minerals from your body.
It's the best water. period.

No matter the source, whether lake, ocean, or tap water, if it is steam distilled, you are getting the same product in the end.  So stop buying water shipped from some fancy place and just buy steam distilled water which has been bottled in transparent plastic or glass bottles.  Sometimes, the opaque plastic bottles, if they were left exposed to direct sunlight, or heat, leave a flavor in the water.  That's plastic your drinking flaking off of the container's interior.

Oh, and yes, thanks to the uncontested Bull Shit about distilled water on the web, my sister thinks I'm about to drop dead for 20 years now, yet she smokes cigarettes...

[IanB]

Can drinking unfiltered water from my kitchen cold-water tap, even waiting several days after a repair event, be dangerous to drink?

In general, drinking "hard" water is harmless, as long as the dissolved minerals are safe (e.g. calcium, magnesium, carbonates, sulfates). Even small amounts of iron are no problem, it will just supplement the iron (a necessary nutrient) in your diet.

You should be able to get an assay of the dissolved minerals from the city or water supply authority to find out what is in your water.

Bear in mind that even tiny amounts of "bad" things like arsenic are no problem, if the amount is small enough. So don't be alarmed by the results of such an assay.

As for dissolved solids, a simple water filter will not reduce dissolved solids. An ion exchange bed might replace calcium with sodium, and carbonate with chloride, but while this will be good for soap and laundry, it will do nothing useful for drinking.

Unless your water quality is exceptionally bad, a water filter is a waste of money. You might need one if your water comes from a well, but if your water comes from the city it will be adequately purified before it reaches you. (Unless you live in bad parts of Michigan.)

Regarding all the brown muck in your plumbing system, that sucks. All you can do is run the water continuously for a long time to flush out all the muck until it runs clear.

[coppercone2]

careful with ion exchange resins, they tend to make nasty organic byproducts. I suspect that the metal ions which are wedged into the resin act like a sort of catalyst (like randy nickle, palladium/carbon, etc), I don't know if the resin itself gets decayed or if residual organics are sometimes reacted to more toxic ones. I believe its if the water you start with is dirty with certain contaminants.

I have been thinking about this kind of system but it seems prudent to install an organic absorbing filter after your ion exchange resin.

I forgot the name of the compound that was found to form in them, it was used for a homicide before. It has medical uses however. I think it was a potential or known carcinogen.

Some compounds, like NMDA, are not removable with carbon filters, and these are known to be produced in IER

https://pubs.acs.org/doi/abs/10.1021/es4003185?journalCode=esthag

https://cdr.lib.unc.edu/indexablecontent/uuid:1d243207-adf8-4a10-b3de-12174391bbbd

when I start reading about this shit I feel like I am playing russian roulette with my taps lol

Distillation is a kind of difficult process too, to make water real pure. You need quite a nice setup.

I just use carbon filters because my water tastes rather harsh without them.

If you are serious about removing organic contaminants you probably need to test the water and get appropriately designed molecular sieves for what ailes you.

[SuzyC]

I seem to be drinking less water than is probably best for anyone just because of the taste.

Even if I boil the water, it still has a less but still noticeable hard water taste. There are no reports in the local news about anyone having health problems with the water, but there must be some reason people would elect Trump for president.

I see on the web DIY under the sink water filters with twist-in filter elements and comes with a faucet and all the plumbing.

I think a filter would be a good idea just to allow me to drink more water.

So I am thinking of buying such a DIY system, one that I can interchange my choice of cartridges at any time.

Three filters available: all have 500gal/6mths life.

What's best?

Level1:  "Ice-Water" 50-micron filter cartridge,   cheapest choice, comes with the whole plumbing kit.
Level 3: Best filter cartridge that is not a RO filter, 5-micron,  99% reduction of many contaminants, costs twice as much as the level 1.
Level 4: RO filter cartridge  .5-micron,  costs almost three times as much as the level 1.

Electron-geeks.. tell me, what do you think?

[IanB]

I'm not sure. Hard water usually tastes nice, not bad. That's why people pay so much for bottles of natural mineral water (which is just hard water in an expensive bottle).

Bad, or "off" tastes, usually come from organic contaminants, or chlorine (or both). These bad flavors can be removed by an activated charcoal filter.

You could try getting a tabletop activated charcoal filter and try it out to see if you like the results before investing in an installed filter.

[IconicPCB]

I need clean water in our process.
To this end we run a cascade of filters consisting of 5 micron sludge filter, 1 micron activated charcoal filter and an RO membrane.

The filtered water is stored in a tank with UV recirculating chamber and resin based ionic exchange filter.

The water is monitored by a TDS in-line sensor and we routinely see sub micro siemens water during and post water polishing run.
The TDS instrument is home brewed and consists of an in line sampling chamber with two parallel aces through which two stainless steel bolts protrude flush with plastic walls.

 I would not drink the polished water it does leach out minerals from the teeth in the first instance and then the rest of the body.

Proof of this is the brass fittings in contact with polished water turn porous after a while.

[NiHaoMike]

What about distill water under vacuum to reduce the temperatures required? I'm thinking of a tank holding a few gallons that can be easily opened for cleaning, a stainless steel condenser, and a small hacked air compressor as a vacuum pump. Going by the (somewhat controversial) 8 cups of water per day rule, it would take about 50W of heat to distill enough water - about as much as a lower end desktop CPU. It's not very difficult to make a vacuum pump that can pull down to 27" of vacuum, at which point the boiling point of water gets plenty low for a common desktop CPU or GPU. That would make an interesting project - a cryptocurrency miner that makes very pure water. Or use a heat pump of some sort to heat the tank and cool the condenser at the same time.

[SuzyC]

A special thanks to IanB.

In fact the taste of my water now is not "bad" but rather brackishly unpalatable, it has a considerable aftertaste that doesn't quite match chlorine like in a swimming pool,  but is nonetheless unpleasant. It is patently hard with lotsa calcium. From what I read on the internet, my area's water treatment plant is using hydrogen peroxide instead of chlorine.

I think I will buy the DIY "Ice Water" under-the-sink system that comes as a complete kit because I've tasted some water from a neighbor\s fridge that has dispenses filtered ice water that is  much better tasting, but even this water falls short of being pleasant tasting, even if it has a much milder aftertaste.

Friends I know that live in a much nicer neighborhood a few miles away have tap water that tastes good straight from the tap, it just tastes like almost pure water, and the reason for this is that they get water form one of the other different water systems that supply different parts of the city.

I know how "sweet" good water can taste because I used to get it delivered weekly in a really big bottle that sits on the ceramic water cooler the company supplied.

[Buriedcode]

I've been drinking and cooking with distilled water for 20 years now.  I call bullshit on it leaching minerals from your body.
It's the best water. period.

I didn't see anyone here claim that distilled water leaches minerals from the body - there were some fears that deionized water might but its hardly solid science.  The only references on the internet on the alleged "dangers" of drinking distilled water were from pseudoscience websites (like health sites and "wellness" crap) that try to sell supplements and distort facts to sell things.

[rstofer]

A special thanks to IanB.

In fact the taste of my water now is not "bad" but rather brackishly unpalatable, it has a considerable aftertaste that doesn't quite match chlorine like in a swimming pool,  but is nonetheless unpleasant. It is patently hard with lotsa calcium. From what I read on the internet, my area's water treatment plant is using hydrogen peroxide instead of chlorine.

Hydrogen peroxide will kill the biologics quickly but it comes out of the water very fast.  Many agencies have changed from chlorine to chloramine and that stuff smells and tastes nasty.  I must be wrong because...

The CDC makes chloramine sound like the end-all be-all of water treatment:
https://www.cdc.gov/healthywater/drinking/public/chloramine-disinfection.html

So, how come it kills pet fish?:
https://www.tampabaywater.org/monochloramine-information-for-fish-owners

[IanB]

The CDC makes chloramine sound like the end-all be-all of water treatment:

So, how come it kills pet fish?

Because you can't always believe what you read from the Center for Deception and Corruption?

One anecdote from me, I just recently filled my empty water bottle from a chilled water dispenser at the airport. When I later opened the bottle on the plane my nose was assaulted with the most foul and acrid chlorine smell imaginable. I don't know what they are imagining when they think people may want to drink that stuff... 

[Conrad Hoffman]

I need clean water in our process.
To this end we run a cascade of filters consisting of 5 micron sludge filter, 1 micron activated charcoal filter and an RO membrane.

The filtered water is stored in a tank with UV recirculating chamber and resin based ionic exchange filter.

The water is monitored by a TDS in-line sensor and we routinely see sub micro siemens water during and post water polishing run.
The TDS instrument is home brewed and consists of an in line sampling chamber with two parallel aces through which two stainless steel bolts protrude flush with plastic walls.

 I would not drink the polished water it does leach out minerals from the teeth in the first instance and then the rest of the body.

Proof of this is the brass fittings in contact with polished water turn porous after a while.

One never uses metal fittings in a DI water system, plastic only. We have a really mediocre system here, geared more towards volume than resistivity, with a single dual content cartridge. It's a lot better than tap water, but nowhere near as good as semiconductor water. Good DI water degrades on exposure to air, so high performance systems continuously recirculate.

No idea if Mountain Dew or Coke or DI water is worse for your teeth.

[rstofer]

Good DI water degrades on exposure to air, so high performance systems continuously recirculate.

One design criteria for the piping system is to keep the flow velocity at or above 100 feet per second at every point in the system.  This is to prevent bacteria from growing in dead legs.

One of the cooler things I did with Excel back in the day (say '88) is flow balance an entire wafer fab piping system using the Method of Residuals.  I don't know how it worked out in practice but it seemed good on paper.  It only took about 3 iterations to get balance.  Very cool!

Yes, I spent a very long time dealing with DI water systems for wafer fab.  Our plant made 300,000 gallons per day back in the days of wet processes.  I'm not sure how much water is used today.  We were transitioning to dry processes back in the late '80s and I changed industries so I don't know where it is today.

FWIW, our goal for resistivity was 18 MOhm-cm.

[IconicPCB]

We used a palladium based hole wall activation process. We did not use it every day so maintenance of bath became an issue and every time it had to be changed it was an expensive proposition.
Colloidal palladium would drop out of suspension producing expensive sludge.
Had to go away from it; the chemical became too expensive when the local distributor ceased holding stocks.

We now use a Russian process based on copper phosphite  pyrolysis reaction.

[6PTsocket]

I've been drinking and cooking with distilled water for 20 years now.  I call bullshit on it leaching minerals from your body.
It's the best water. period.

I didn't see anyone here claim that distilled water leaches minerals from the body - there were some fears that deionized water might but its hardly solid science.  The only references on the internet on the alleged "dangers" of drinking distilled water were from pseudoscience websites (like health sites and "wellness" crap) that try to sell supplements and distort facts to sell things.

It sure can't hurt you but for drinking it tastes like #/=÷. It is the dissolved salts that give water a pleasant (or not pleasant)  taste. If the dissolced salts are below a certain number it is legally spring water and if higher it is mineral water. The tap water in some places qualifies as mineral water. Coke and Pepsi (Desani and I forget the other one) synthasize their spring water by deionizing and filtering the local tap water and then adding a standardized mineral packet so it tastes the same everywhere. The problem with TDS detectors is the do not respond to all contaminents, like insecticides.

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