How to prevent TDS Creep, anyone?

[Bart]

Does anyone here know how to prevent TDS creep in the r.o. membrane housing when system is in shut down mode?

I know when concentrate water sits in there for a while it will creep to the other side of the membrane and consequently gets sucked away by the fridge ice maker -- now I've got ice cubes with 200-300 ppm -- yikes!

[Andy CWS]

A membrane flush is the only way you can prevent this. I know of one RO for residiential applications that has it. Everytime the tank fills up, 140-200ml of RO water flushes the membrane. So the water can sit there for extended periods of time and the creep stays away.

I don't think your can be modified to do that. Stagnant water is a major reason for membrane failure.

Since the water to the fridge (as well as the faucet) comes from the tank, why does the TDS go up for that only? How long has the fridge been hooked up to the RO?

Andy Christensen, CWS-II

[Bart]

A membrane flush is the only way you can prevent this. I know of one RO for residiential applications that has it. Everytime the tank fills up, 140-200ml of RO water flushes the membrane. So the water can sit there for extended periods of time and the creep stays away.

I don't think your can be modified to do that. Stagnant water is a major reason for membrane failure.

Since the water to the fridge (as well as the faucet) comes from the tank, why does the TDS go up for that only? How long has the fridge been hooked up to the RO?

Andy Christensen, CWS-II

Thanks for responding on a Sunday, Andy. I really appreciate it.

Basically, the r.o. in the house is always on a short cycle mode - only a glassful is drawn at a time and most of the time in the afternoon and at nights when nobody is around, only the fridge ice maker draws water from it. The problem I've discovered is when the system just sits there for maybe 15 minutes or more, tds starts to creep in. I know because I had a 2-probe tds meter hooked up to the unit. The reading at the pure water line after the membrane canister normally would be in the low to mid 20s ppm, but when it sits there for 30 minutes and longer AFTER it shuts off (tank already full and no draw), the creep would spike up to the 100s and and even higher the longer the inactivity drags on. Worse, the rate of the creep would increase if there is pressure on the feed line to the membrane unit. What I did to stop this was to shut off the valve on the feed line to the unit because mine is only equipped with a permeate pump which only stops the pure water and brine lines not the feed water. But before shutting the feed line off, I had to purge the unit of the contaminated water that has accumulated in the membrane housing up to the portion of the pure water line with the tds sensor on it, and let it fill up the tank and shut itself down. When it did, I turned the feed water valve off and let the water just sit there inside the membrane housing. I checked the tds reading at the pure water line just outside of the housing and it stayed at 30 ppm. I didn't let this fool me because I know that the pure water side of the membrane inside the casing is slowly being invaded by tds. After waiting for about an hour, I opened the r.o. faucet full as soon as water came out the tds count surged from 30 to 200+ ppm - not a surprise there. I waited until the count went back down to the mid 20s and stabilized then I shut the faucet off. What I have learned from this experience is, with or without pressure, when water is not flowing inside the chamber there is always TDS creep. All reverse osmosis out there has this problem and only a small percentage of r.o. owners know this.

Flushes are good for cleaning the membrane surface of contaminants. If it is done with non-ro water (e.g. unpurified, before-membrane water), TDS will always be present. The only exception to this that makes sense would be if you flush the membrane with RO-filtered water or you let RO-filtered water sit inside the chamber i.e. both sides of the membrane filled with ro-filtered water, no matter how long you wait for the creep to happen, there will be no creep because ALL the water inside is already purified. I've heard that the Kinetico K5 does this. Can you confirm?

[Andy CWS]

YOur research has shown what happens to many ROs. Are you sure you have TFC membrane?

To answer your question, yes, the K5 unit does flush the membrane whenever the tank fills. I uses a reserve in the sub-assembly and flushes in strong pulses that you can hear. This is one of the reasons why Kinetico gives up to a ten-year warranty on the membrane.

Another thing is that the tank on the K5 refills even after taking a small amount of water. Bladder-style tanks are nearly empty before they start to refill.

USEPA recommends 0-50ppm to ideal for drinking water.

Andy Christensen, CWS-II

[Bart]

50GPD TFC - positive NOT CTO.

Are you sure about the 10-yr. membrane warranty? That sounds too good to be true I mean no catch or fine prints? There has got to be.

I've been slavin' all day looking for product specifications on the K5 on the net but can't find one. How big is the unit including the tank i.e. dimensions l x w x h? How much is it and what's the cost of replacing the filters annually or semi-annually? If the unit needs servicing - how much is the labor cost including parts? Can I install the unit myself or does it have to be the dealer?

[Andy CWS]

Then warranties are 10-years if follwong a Kinetico softener, new or existing. That included all parts and membrane. Filers (on top of the unit) are the responsibility of the owner. It has a four-year warranty on the membrane if it follows a non-kinetico softener. Still ten years on the parts.

Mounted on WALL, three-gallon tank with 2.7 gallon capacity. All lines are 3/8"


They designed to fit under the sink, sitting on the floor or mounted on the wall. can get you more specific demenions if you'd like.

"strings attached, fine print?" No warranty is unlimited.

Filters are metered. How long would it take you drink 500 gallons of water? It takes my family about 14 months with cat, dog, plants, coffee, tea, a lot of Asian cuisine. Costs vary from dealer to dealer but around $60.00.

Andy

[Bart]

Wow...thanks for sharing that photo. That black tank sure looks like a mini softener tank.

Okay, I want to get this straight. With a Kinetico softener, 10yr. warranty on the membrane and the unit. But with a non-Kinetico softener, only 4yr. warranty on the membrane and 10yr. warranty on the unit?

When you say 'filters are metered,' you mean the K5 has a flow meter so when it reaches the 500-gallon usage mark it's time to change the filters? I think 500 is way too short -- generic r/o systems typically have filters that last in the thousands not in the hundreds.

"Costs vary from dealer to dealer but around $60.00" -- Sixty dollars for all of them or for each one? I pray it's not the latter.

I would appreciate if you can give me the exact dimensions of the tank and the K5 so I will know if it will fit under my sink cabinet which is kind of small for a standard sink. Since it's using 3/8, can I use my existing 1/4 r.o. faucet with it? I have all the fittings to make it work. Is the drain line also 3/8?

[Andy CWS]

Warranty info is correct.

The membrane should last for thousands of gallon but mant manufacturers recommend changing pre- and post-filters every six months. Kinetico's research and lab tests show for optimum performance, filters should be changed every 500 gallons. With all other systems I know that don't have any indicator of folter life becomes a guessing game at when to change them.

There is a flow meter that measures volume not flow rate. It is incorporated in the final filter so it meters all the water that comes to the faucet or fridge. By replacing with a new filter the metering indicator automatically resets.

Cost estimate is combined. Additional "flex" filters/cartridges would increase costs as well as performance.

Not sure about your 1/4 faucet and whether the back pressure will affect performance. If comes with very nice faucets in a variety of metels.

http://kineticoencyclopedia.com/DataDictionaryAssets/Datasheet_K5_Drinking_Water_Station.pdf

Hope that helped.

Andy

[Bart]

Thanks for the link and the photo.

I don't really think back pressure would be a problem -- a faucet, no matter if it has a 3/8 or 1/4 connection if you open it partially, you are still restricting the flow of water which creates back pressure. That's only my opinion but it makes sense, doesn't it?

Wow, 2 filters for $60 -- $30 each, now that's expensive.

When you buy this K5, can you opt for installing it yourself or does it have to be installed by the salesman? The reason I'm asking this is because I don't want to risk the salesman damaging my sink cabinet. The last time I had somebody messing around under it, he made some dents and dings and some minor leaks.

[Bart]

By the way, don't you think 1 filter before the r/o membrane is enough to protect it from contaminants? Conventional r/o systems normally have a sediment followed by 2 carbon blocks before it. Since the K5 uses granulated carbon, it's a bit inferior to carbon block in terms of performance. What do you think?

[Andy CWS]

I believe you're right; fridge lines are 1/4" anyway.

Salesman probably wouldn't install anything. That would be the service guy. Yes, you can install it yourself as long as you have basic tools and you can get instructions. Ask about warranty, though. You may need to have a service guy stop by and double check everything.

No granulated filter is placed before the membrane. It is either a 5-micron sediment (on well water) or a 5-micron sediment/carbon on well. This singular pre-filter has proven very effective. The only time I would put an additional pre-pre-filter is to fight small amounts of sulfur gas coming into the unit.

Two post filters are available: A standard granual activated carbon or a VOC carbon block filter.

Yes, I have seen those 7plus stage ROs. Not sure why they do that but it won't help with TDS creep, will it?

Did you get the dimensions?

Andy

[Bart]

Fridge lines are 1/4 if the fridge is 10 ft. or less from the r/o and 3/8 if more than 10 ft. to compensate for loss of pressure when running smaller diameter tubing over long distances both horizontal and vertical. Most fridge runs nowadays are 3/8 because newer models with built-in crappy filters need that extra push to make them work and some solenoids are very sensitive to low pressure, hence, a 3/8 is more practical than a 1/4.

I've always believed that the more filters involved in the filtration process, the better quality water you can get out of it. It's true that no matter how many filters you string together there's always TDS creep -- it's a long standing issue with all r/o systems out there. Even reefkeepers who always have in their disposal the deionization filter to totally eliminate TDS often find themselves at the mercy of it. DI filters are expensive to maintain and they can easily wear out fast depending on the amount of TDS that goes past the membrane. TDS creep only happens when both tap (containing high amounts of TDS) & purified water are standing on either side of the membrane filter. It can increase rapidly in minutes if there is pressure on the tap water side. The only case where there will be no creep is when both sides of the membrane have pure water. When I say there's no creep it doesn't mean that no TDS is present. Purified water sometimes contain little amounts of TDS depending on the membrane's rejection rating but in this case it is controlled.

Kinetico has a very unconventional way of flushing the membrane. Instead of using tap water as other conventional r/o systems do, it uses purified water to rinse the membrane's surfaces of contaminants. Using purified water to clean the dirty side of the membrane totally eliminates this TDS creep problem. I have yet to see this in action.

[Bart]

Yes, I got all the dimensions and thanks for the link.

Also, I have already set an appointment with our local Kinetico dealer to test our water this Friday.

[Andy CWS]

I have yet to see this in action.

It's not likely that you will see this...but you can hear it. As the tank fills, you can hear the whoosh, whoosh, whoosh of permeate water stored in the sub-assembly flush down the membrane. It's a very cool feature.

Glad you can appreciate it.

Where are you located?

[Bart]

Nanu nanu Florida.

Have you tried testing the water for TDS right after a long period of standby -- like an hour or two? Was the level the same as when the unit was running normally in between draws and refills?

Does the k5 use a Dow Filmtec membrane?

After it "whoosh-whooshes" itself with purified water, does the chamber stay empty or gets filled up with tap?