Mcallen, Texas
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Update by user Dec 20, 2016

OK, after a year and half of continuous experience on the Zero Water filter and browsing all replies following my review so far, I think I have a deeper understanding of the "problem" of this product.

I mentioned that the TDS reading of the tap water in the city I was living (McAllen, TX) was about 700 and each Zero Water cartridge did not filter more than 5 gallons of water there.Now I have moved to the Nashville area in TN, where the TDS of tap water is just a little over 100, indicating much less ions contained in the water (very good quality).

The old cartridge which already filtered 2 gallons in TX continued to give me about 15 gallons more of clean water in TN before it turned sour. Then I tried with a brand new Zero Water cartridge and it has filtered 28 gallons of water and so far it is still keeping the TDS reading at 0 after filtering. Therefore, the acidic taste at the end of the lifetime of a filter cartridge seems to reflect a capacity "problem" instead of a quality problem.

To further explain this "problem", the cations (ions carrying positive charges) and the anions (ions carrying negative charges) in water are always equal in the number of charge. Cations may include calcium ion (Ca 2+), sodium ion (Na 1+), potassium ion (K 1+), magnesium ion (Mn 2+), and so on.

Anions may include sulfate ion (SO4 2-), chloride ion (Cl 1-), carbonate ion (CO3 2-), and so on. The numbers at front of + and - signs denote the number of charge each ion carries, but this is not important if you don't care about the detail. The Zero Water filter contains an ion exchange layer, which replaces the cations with hydrogen ion (acid ion, H 1+), and replaces the anions with hydroxyl ion (basic ion, OH 1-). As you may already know (H+) and (OH-) form pure water H2O.

This is how the filter gives you pure water. Everything is fine until either ion, (H+) or (OH-), is depleted in the cartridge. In our case the hydroxyl ion (OH-) is fully consumed first, and then the anions remain in the water after filtering, and the cations are still replaced by the hydrogen ion (acid ion), finally resulting in acids, such as sulphuric acid (H2SO4), hydrochloric acid (HCl), carbonic acid (H2CO3), and so on.

That's why the water tastes sour or acidic at the end.

Finally, my suggestion is, if the TDS reading is high in your area, it may be economically preferable to just buy water from supermarkets.If the TDS values is low, Zero Water is a convenient option.

Original review posted by user May 23, 2015

I am a chemist and a polymer expert. I know what ion exchange is. I had the same sour/acidic taste experience with ZeroWater. It seems to me a design problem of this product.

Background 1: What does a filter capture?

Many other branded filters, such as Brita, DO filter some harmful organic chemicals in water using activated carbon. They don't do anything with the salts in water (not only the sodium chloride used in cooking). General salts in water are not harmful, but they don't taste good at a high concentration. ZeroWater captures cations and anions in water using the ion exchange technique, so that the salts are filtered.

Background 2: What do you know from TDS number?

The TDS meter coming with ZeroWater tests the conductivity of water. That is, it only measures the concentration of salt/ion in water instead of all solids, and estimates the amount of total dissolved solid in water. The water with a 0 reading on the meter can still contain some organic chemicals. Anyway, it's reasonable to believe the total solid left in water is very close to zero based on the so-claimed 5 stage filtering technique including an activated carbon layer. However, a totally pure water is not good to health in fact. If you read a TDS value of 30 from a bottled spring water, it doesn't mean the water is not good. Instead, the water contains some minerals/salts needed by your body. Sometimes I added a small fraction of Brita filtered water in the ZeroWater to tune it to below 50 TDS.

Problem of ZeroWater:

After flushing the ZeroWater filter I started to enjoy the filtered water, which was much cleaner than the tap water (TDS around 700). However, after about 5 gallons of water were filtered, the filtered water turned bad and tasted extremely sour/acidic as many people had experienced. I noticed at that time that the flow rate of the filter was faster than before and some gas bubbles came out from the orifice at the bottom of the filter. The sour taste indicated there might be still a large amount of hydrogen ions available in the filter, and the filter should still have a considerable lifetime. It seemed that some structure in the filter was crushed because of the build-up of filtered substance or increased pressure inside, so the chemical holding hydrogen ions leaked out. The flow rate might be much faster due to the damage, taking out the small amount of air that would be otherwise locked inside the filter.

Hope this comment is useful to both the users and the engineering department of ZeroWater.

Review about: Zd 018 23 Cup Water Dispenser.

Review #640338 is a subjective opinion of a user.

Zerowater Filter
Reason of Review / Monetary Loss Bad quality / $40
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Tempe, Arizona, United States #1264156
We have exactly the same problem. Just 4 days, the water is not drinkable. We are in Arizona. Not sure what is Walmart's refund policy for this ***. I will bring it to Walmart for a refund tomorrow.
Lafayette, Colorado, United States #1261164
Hello! Thank you for this explanation. The water were I am at is decent at 154 TDS says the zero water site. I haven't purchased this system yet nor tested my specific water out of the tap.
My question lies within a double filter method proposed by a reviewer on amazon. He suggests to use a first stage zero water filter past it's normal lifespan of 006. Then you will have a second stage filter that gets a fairly low TDS water. This way the second stage filter will last a long time. Then once the secondary filter gets to 006, you move that one into the first stage position and put a new filter as the second stage.
I am wondering, based on your review of how the ion exchange can become unbalanced, if you think the dual stage filtering is a bad idea. Do you think that the water from the primary will cause an opposite imbalance in the ions of the secondary filter and make the water harmful in some way? If so, do you think this would only be an issue with water of a very high starting TDS or even doing the dual stage for lower TDS will still cause this imbalance?
to Kirk Mcallen, Texas, United States #1261473
Hi Kirk! The two-stage filtration is a natual solution that people would figure out to last the lifetime of the filter cartridges. This will be very helpful if the first depletion of an ion source is random between hydrogen ion (acid ion) and hydroxyl ion (basic ion). However, it seems so far that the basic ions are always depleted sooner than the acid ions, based on all reviews I have read. In this case the two-stage filtration system can save a large number of acid ions in the cartridge at the second stage. The number of basic ions saved by using the two-stage filtration system depends on how quickly the TDS turns bad from 1 to near the value of tap water, i.e. how many basic ions are left for the final extraction. Generally, this is not a long process when the ion exchange layer gets to the end of the lifetime. Other than the ion exchange layer, the active carbon layer may be also saturated by contaminants for an extended filtration if the contamination in the water is high. The clogging will slow down the stream.
As a conclusion, the two-stage filtration system helps to a small extent to extend the lifetime of the cartridge, and I don't expect harmful materials if the final TDS is 0. This is based on the assumption that the sour taste comes from the early depletion of basic ions.
By the way, I generally change the filter cartridge once I notice the sour taste (TDS is 1 or 2). I don't like that taste and I don't think drinking sour water is good for health,
... Show more
Phoenix, Arizona, United States #1250319
Nothing has changed, its Dec. 2016 and the filter has only cleaned about 3 gallons of water before the turning distasteful. If I had known the filter was so short lived I would not have purchased this Zero Water jug. I purchased from Walmart in San Diego for $31.88 + tax. I got approx 3 gallons of fresh tasting water. I could have purchased 30 gallons of clean water for that price; or .50 cents for 5 gallons in Yuma AZ.
I wish I had read reviews before purchasing. And the only thing I can suggest to the co. for good customer service is offer filters at a very low price since we who own these need to be thanked not gouged. I suggest they offer 1st. time orders a very good deal or there will be no ordering of replacement from this customer.
to RVsnowbird Ottawa, Ontario, Canada #1252015
Similar situation here. About $30 for two filters here in Florida, and it only filters around 5 gallons before turning sour.
to RVsnowbird #1255679
I agree. No one will pay $5 a gallon for clean water no matter what the taste. I will just fill my pitcher for 25 cents a gallon from a water machine.
Somerset, New Jersey, United States #1248498
This did not help me at all.
Stoughton, Massachusetts, United States #1220378
I drank sever glasses with my new filter. I noticed the taste getting acidic and finally found your comment. It's been several hours and I feel a burning, it's not even lessened! What is the chemical you mentioned as possibly be leaked out of the filter? Thank you!
Plano, Texas, United States #1218181
Same here. After only two weeks of use the water has become so sour that it's not even drinkable anymore. I am disappointed of the poor performed quality of Zero Water.
Vista, California, United States #1212787
Cool Info!

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