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on February 17, 2012
I ordered the TDS-4 after reading several reviews on it and other products as well as comparing the specs to its rivals.

I read all the specs for each tester I found and it came down to this TDS-4 and the TDS-EZ. The determining factors were its accuracy and ATC. The TDS-4 has a stated accuracy of +/- 2% as opposed to the +/- 3% of the TDS-EZ. The TDS-4 has ATC (Automatic Temperature Compensation) which comes in handy since water can be different temps. Each had the same hold and auto-off function and read in 1 ppm for the first 999 and 10 ppm for 1000 - 9990.

One disappointment I had with the TDS-4 was that it didn't have a "How pure is your water?" chart on the back like the TDS-EZ. It's not hard to remember what's on the TDS-EZ chart, but would be a nice-to-have. Instead I just remember that 0 to 50 is what my RO system should be at, 50 to 100 are carbon filters, 100 to 200 is hard water, 200 to 400 is average tap water (200 to 300 being marginally acceptable drinking water), and that 500 is the EPA's max level it should be (Source: TDS-EZ chart).

I originally ordered the TDS-4 to test our new RO (reverse osmosis) under counter filtration system (Watts Premier WP-4V). Now for my experience with the TDS-4, when I received the unit from Amazon I immediately tested my RO system first (29 ppm), then my tap (251 ppm), and finally RO water from a local watershop (2 ppm). My RO system was in mid-range of the 0 to 50 acceptable for RO systems, my tap was in the mid-range of acceptable tap levels of 200 to 300, and the water from the watershop was almost pure water. I'm pleased with my RO system compared to the watershop since they have huge filtration systems and the WP-4V takes up less than half of my cabinet under the sink; although, I do wish they tasted identical, the WP-4V tastes good, just not perfect like that from the watershop.

I did another test at my employer who a filter on the drinking water, the result was 221 ppm, I knew it was bad, but expected better because of the filter which I don't know what kind of filter it is. Needless to say I'm bringing in my own water for now on since the water from their tap was 240 ppm.

I ordered the TDS-4 from Amazon Prime and received it in 2 days in perfect condition. I would definitely recommend this to those who want an estimate of what the level of TDS is in their water, it will also come in handy to show the life of our RO filters.
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on November 10, 2010
I have a reverse osmosis water system for drinking water that's about 3 years old. I was about to replace the filters because the manual says to replace them every 3-5 years. Good thing I ordered this $25 tester. It's about the size of a highlighter pen, has a clear number display, and is super easy to use. You test the water out of the tap then test the water out of the RO system. Divide the RO number by the tap number to get a percentage. As long as it's under 20% you don't have to change the membrane filter. My percentage was 5%, which means I've probably got a few more years before I need to change my membrane!
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on December 16, 2012
I have found the writeup for HM Digital TDS meter model TDS-4 and TDS EZ is poor in that the distinction between the two TDS meters is not apparent in the Amazon write up. For those who are interested TDS-4 is temperature compensated and TDS EZ TDS reading is not temperature compensated, meaning TDS-4 should give you less variation in TDS readings.

Ok I cannot put the web URL in, Amazon does too good of a job finding that you have put a web link in. I will place the URL location vertical:


Also you should know the TDS-3 does everything the TDS-4 does and it also reads out temperature, TDS-3 is not a slim design though.
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on October 20, 2011
This meter works great. I wanted to check the hardness of my home water so a TDS (Total Dissolved Solids) meter will give a rough indication of hardness. I ordered the meter and it came within a week. I just purchased a TDS meter from Fisher and tried both of them at the same time. I rinsed out a cup with water (several times) then filled the cup with tap water. The HM read 185 ppm and the Fisher meter read 430 ppm TDS. I thought wow, somebody is wrong. So I took both meters back to the laboratory I work in. I prepared a 292 ppm TDS standard from dried NaCl and ultra high purity DI water. The HM meter read the standard as 287 ppm and the Fisher meter read the standard as 410 ppm.
I guess you don't always get what you pay for. The $20 HM was way more accurate than the more expensive Fisher TDS meter.
Both meters work and the Fisher meter can be re calibrated but why spend more money when the HM meter works great.
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on March 22, 2011
This review is on both the meter and the calibration fluid designed to calibrate the meter.

I bought the TDS-3 from Amazon as a check on the efficacy of my Brita filters. Shortly after I bought it I misplaced it (don't ask, it's a lesson in applied stupidity) so I bought another. You guessed it; I found the first one immediately after the second one arrived.

Having the two meters did provide one benefit though, I could compare the two. I was quite disappointed to note that there was a significant difference between readings for the two meters.


If you have this meter, be sure to go to the web site for the manufacturer (Google TDS-3). They have an excellent discussion on how to use the meter to take measurements, what the meter's limitations are, i.e., what it measures, and how to calibrate it.

Using their instructions, i.e., taking measurements correctly, the two meters were much closer in their measurements. There was from 2 to 3% difference in the numerical readings for tap water, Brita-filtered water and distilled water. Both read zero for distilled water. Not too bad for home use. It's really important to do it right, though.

Since there was a difference between the two meters, however small, I decided to calibrate them using TDS's own calibration fluid. This is a mixture of water and NaCl to a known concentration. They offer 1000 ppm and 342 ppm. The TDS-3 is supposed to be calibrated against the 342 ppm fluid.

Amazon offers TDS calibration fluid. The product is pictured with two bottles, one at 342 ppm and behind it in the picture, 1000 ppm. Since the 342 ppm was in front and much larger, I assumed that's what would be sent. Well...we all know about assumptions.

The fluid I received was the 1000 ppm. When I contacted the company the representative said 1000 ppm was all they offered. This disagrees with their web site but I didn't press it; it's not that expensive (shipping was almost as much as the fluid itself) and I made some 333 ppm fluid by diluting what I had 3-to-1 with distilled water. The meters read low with my jury-rigged calibration fluid, 304 rather than 333. Not tremendously scientific but good enough for my purposes. The company did offer to take the fluid back - with me paying for shipping.

So I have rated this meter 3 because of the misleading approach to selling calibration fluid, the claim that they only offer 1000 ppm, and the discrepancy between the two meters when their web site says "no need to calibrate out of the box".

The meter is OK for my purposes. I can measure filter efficiency relatively rather than absolutely. I don't need precision; it's good enough to note that the filter reduces TDS without actually knowing the precise value of the reduction. In short, if I lose both of these (not inconceivable) I'd buy another.
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on October 5, 2010
Being curious about the effectiveness of my Watts R. O. system I bought the HM TDS meter to test the dissolved solids. The incoming water showed 240 ppm. When I checked the R. O. Output it read the same. The Watts tech suggested I check the R. O. Flow Restrictor for a punctured diaphram. That was it. After replacing it the water tested 25 ppm soon after. The device did the job I needed done!
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on February 28, 2012
It works, but you can only dip the very tip in. Why? Because the base (yes the part you put in the water) is not WATERPROOF! So if you have slightly too much water, and accidentally drop it in for a second slightly beyond the limit, the device fills with water. This ruins the device. So be VERY careful with this thing if you decide to buy it. I will not be purchasing another one.
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on March 31, 2010
If your aim is to check on the performance of your home water filtering system when fed by a municipal water supply you don't need anything more. Using it to determine whether a clear mountain stream is safe to drink or if your water well has been contaminated by the waste storage facility down the road is quite a different matter.

There is a cheaper TDS-EZ version which looks the same but does not have a thermometer nor does it offer temperature compensation (doh). Plus this one has a case. Big whoop, I know. HM Digital has a selection guide to hand held testers at [...] with all the details. What else is there to say? It is accurate, it lasts and it's cheap. You don't often get that combination anymore.
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on January 6, 2011
I was about to replace the filters in my reverse osmosis system, based on how long they have been in service. I bought this meter to verify the need for RO membrane replacement.

We have extreemly hard water in our area, tap water reads 450ppm TDS, and Reverse Osmosis filtered water reads 15ppm. 450-15=435 435/450=.966 .966*100=96.6% So, my reverse osmosis is running at 96.6% TDS reduction. I just saved $100 in replacement filter cost. I will still replace the pre/post carbon filters based on water taste, and service time, however the carbon filters are far less expensive than the RO membrane.

I am very pleased with this purchase.
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VINE VOICEon November 27, 2008
It seems to work.. I have no way to gauge if it is truly accurate. :) However, when testing a water source before and after it entered our RO filter, it clearly showed that the RO filter was working. Have had this for about 4 months now and it has worked fine w no battery problems.

It is good that it has a button to save your reading until you take it out of the water. Without that, sometimes it's hard to read the display while the meter is in the water container.
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