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Why is the TDS on my RO system so high?

by Mark Timmons November 20, 2013 49 Comments

Dear Sir,

With your 40 years experience in drinking water, I'm hoping you can help. At this point I'm worried and confused about the new drinking water system we just had installed in our home by a local company that we will be renting from.

For the past 17 years we have been renting a Reverse Osmosis system (4 Stage) from a company that does supply or install ro/alkaline filter equipment. Our equipment is under the kitchen sink. I thought RO water was healthier for myself and my family. I recently read that RO water is Acidic water because it takes all the minerals out. I was told by a friend that adding an Alkaline filter to our RO system would make the water more alkaline which is healthier for the body. This past Wednesday, I had a 6-Stage Reverse Osmosis/Alkaline Ionized Water filter system installed by a different company. I read it would be healthier because the alkaline filter adds Minerals back into the water which makes the water more Alkaline. Drinking a more alkaline water supposedly makes the body less acidic.

The RO water I had before always tested between 10-20 (company serviced every year or sooner if needed). I have a HM digital TDS meter tester and would check it myself now and then.

The new company is family operated. The wife did a lot of research before adding this alkaline ionized filter to their RO systems. She claims it's one of the best filters out there. Her older son takes care of the water system for the military so I thought this was a great testimonial.

Before they installed our new system, we tested my water from my "old" RO water system, it tested 12, both on my tester and his. After our new RO/Alkaline Ionized filter water system was installed it tested at 49. He said it's higher because of the minerals added back into the water. He also told me to drain the tank tonight and in the morning re-test the water, it should be much lower probably in the 20's. In the morning it was 72. This made me worried about drinking this water. I called the owner and she was surprised that it was that high & said she would call the manufacturer and get back to me. I tested the water again this morning, and it's even Higher, 96. As I said at the beginning of this long email, I'm worried about this water and don't know if we should be even drinking it.

When I saw your site and with all your experience in this field I thought you could tell me what's happening & if we should be drinking this water. We also buy bottled water to take out with us. We buy "DaSani" water. I tested the DaSani, it was 24. DaSani claims they add a very small amount of minerals back into their RO water for taste. I thought 24 is a pretty good # for bottled water. Which makes me more confused as to why my new system is testing out so high.

I hope you can help. I would be more happy to pay you a fee for your unbiased opinion on this water situation, please let me know. It would be worth it for someone with your experience.


I.S. - Westlake Village, California

The Water Doctor responded:

First of all, the debate about Alkaline verses Acidic water is sad, because most people do not understand the difference, and there are lots of unscrupulous companies competing for the business. For the record, I do not think a few points on the pH scale make a difference because you drink the water and the water penetrates the cell wall, it becomes the pH of the body anyway.

You have evidently purchased a reverse osmosis system that adds minerals back to the water (usually calcium carbonate) which is why your TDS is higher than before. Your RO is taking the minerals out and the re-mineralization filter is adding some back. It is functioning perfectly in all likelihood. No matter what the label says, you do not have a Alkaline Ionized filter. You have a RO system where additional minerals are added which adds TDS (Total Dissolved Solids) back to the water.

Some manufacturers say that they have ionized alkaline water, but unless the ORP (Oxidation Reduction Potential) is lowered and the pH (potential of Hydrogen) is raised and alkalinity added, you cannot change the alkalinity. The water may be alkaline in nature (pH above 7.0) but it does not add alkalinity and there is no benefit to that.

The people you bought the RO from are probably innocent of any deception, simply uneducated about these things, but just adding minerals to raise the pH (and TDS) really does nothing. To have alkaline water, you would have to use an alkaline water ionizer (an electrical device that uses electrolysis), but that may not be wise either, simply because you can't use RO water to make alkaline water. You have to leave the contaminants, and then you concentrate all the impurities removed by reverse osmosis. A good ionizer can cost up to $7,000.00! Silly, in my opinion when you can simply do one of two things:

  1. Use 1/2 teaspoon of baking soda in 12 ounces of water once a day; or
  2. Use Gerolsteiner Mineral Water once a day.
*I am not a medical doctor (well I am a water doctor) and this is not medical advice, but Alkaline Ionizers are not the solution. The two above methods can produce true alkaline water, but you are not getting it from your reverse osmosis system. You may want to read, a previous blog post I have written on Alkaline vs. Acid Water.

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June 17, 2019 Mark Timmons

That is not even close to good. Call our technical support department to troubleshoot!

December 22, 2019 Roy StJohn

Just replaced 1 sed 1 carb 1 10gpd membrane in old 3-stage RO setup, fully sanitizing and rinsing each housing.
Newly calibrated TDS meter, cross-checked with new ZERO water filter output.
Tap ppm ranges 550-600.
New R.O. filters ppm 550-600 following 25+ gallons of flushing and having double and triple checked for tight membrane insertion.
I am GOBSMACKED at these results!
Any thoughts on what has gone wrong here would be GREATLY appreciated by my entire family and our pets!

December 22, 2019 Mark Timmons

Something is obviously very wrong. If you bought the filters from us, please call our Tech Support Department at 800-608-8792 on M-F from 8 AM to 8 PM EDT.

January 16, 2020 Sumit

TDS of my tap water is 97 and after filter, TDS is only 7. I am using kent RO
What is problem ??

January 24, 2020 Mark Timmons

I would say nothing is wrong. Try emptying your tank on a regular basis and realize that a TDS Meter is within 5% = or -. You are getting over 90% rejection.

February 02, 2020 Nisa

hi, i recently purchased a water filter that us 4-stage filter (pp sediment, granular carbon, Block Carbon & UF Membrane). i took a sample for TDS reading. i noticed it is higher than my tap water. tap water : 175 ppm, after filteration : 350 ppm. how is this possible? does the filters add more mineral to my water?

March 15, 2020 Mark Timmons

It sounds like something si defective or not hooked up properly. Can’t you contact the manufacturer?

March 15, 2020 Phyllis Freeman

We just had a new puromax ro 5 stage installed. The sink water is 440 or so and the ro tests sometimes at 109 and once at 77. The company says it is fine. The plumber is willing to return the unit and purchase another one. We are very confused if our brand new ro is functioning. we have a brand new whole house water softener and brand new acid neutralizer as well. Can you comment? Can we drink this water?

March 15, 2020 Mark Timmons

Most RO systems are made of Chinese parts. They may be assembled in the USA, but all of the parts, including the filters, housings, tanks, and faucets are from the Far East. In the next week, US Water Systems will release it’s 100% All-American RO whereby everything is made in the USA. I’d wait for that… but I am biased!

March 26, 2020 Ann

We just changed our whole reverse osmosis by buying new tank and new filters and membrane (supposedly made in usa).The filters/membrane we bought now are the same as the ones used previously. The problem we have now is that the tds measure really high,way higher than the tap water we have ,which usually measures between 159 and 162.Our reverse osmosis’s tds is now over 200.We had readings from 800+ to 150+ and now to over 200.The water taste really good though,like fresh.I grew up on the farm in eastern Europe and we only drank fresh well water,so I know what fresh taste like.
What could make the tds numbers so high?Our reverse osmosis is a 5 stage as I don’t see the point of adding all those expensive,extra filters that don’t make any sense.We do have mineral drops that we could add to our water,but I concentrate on healthy food to get them from first.

March 27, 2020 Mark Timmons

There are several things that can cause this. I will put up a blog about this in the next couple of days.

June 21, 2020 John Winter

I’ve been drinking well water with a TDS of 750 my entire life. Never been sick one day of my 87 years. Quit worrying about TDS and live your life.

June 21, 2020 Mark Timmons

Well, there you go. That proves that high TDS water is good… right? LOL

September 19, 2020 Mark Evans

Hello. I just had an RO system installed by a company called ECOWATER SYSTEMS. My TDS runs between 8- 16. I paid for two extra filters. 1. Alkaline and 2. Mineral. Now I run just under 40.

What I want to know is, am I wasting my money with the purchase of these two dinners of you can truly change your bodies ph with water and if you can’t get a significant amount of minerals from water?

Should I be getting all the minerals I need from vegetables or the concentrated have mineral drops from a health food store or what?

Because I would rather have my TDS back down to 8-16 again.

Thank you

September 22, 2020 Mark Timmons

Water is not a significant source of minerals. We get most of our minerals from food and supplements. So, remineralizing is of little value. However, most people equate minerals and pH with alkaline water, and that simply is not true. We have a process called Livation Hydration Technology that does produce true Alkaline Water. It does add some trace minerals back in the process, which is necessary to produce alkaline water, not because of the value of the minerals. Our LIvation process does the following: 1. Uses far-infrared balls to emit minerals 2. Increases the pH of the filtered water typically to between 8.5 – 10.0 3. Changes the oxidation-reduction potential of the water (ORP) to between -100mV and -200mV 4. Reduces the sizes of the clusters of water molecules (re-structures) so that the water is easily absorbed in the body 5. It also puts beneficial alkaline minerals into the water, such as calcium, potassium, magnesium. 6. Adds molecular hydrogen with antioxidant potential You can read about it here: It seems to me that there are benefits of alkaline water, but we are not making wild claims. One of the most important things is to have good, clean, pure water, and no other process removes a broader spectrum of contaminants than Reverse Osmosis.

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