R.O. water filter install question

[colemj]

Are you using this to take water on-board, or to use water from your tank? If from your tank, then you will get 20-25% usable water from the amount you can store. The remaining will be tossed as waste. So for example, if you have a full 100gal tank, then you will get 20-25gal of water out of it. So you in effect have a 20-25gal tank now.

This could be OK if you are just short-sailing and don't need a lot of water between being able to fill the tank again.

Your drawing shows a storage tank, but no clear way to use that water or get it out.

One thought is to plumb the waste discharge back to the water tank. This will give you most of 100gal capacity back. It's not like this is seawater, where the brine levels would quickly escalate to the point of exceeding the system capacity. Every so often, completely empty the tank and refill. It is going to dilute anyway every time you fill the tank, so should be able to get several exchanges before complete empty.

Mark

 

[jssailem]

Mark’s idea could work. It would be like washing your hands in progressively dirty water. At some point the cleaning process might be overwhelmed. It is certainly a process that could be tested. You would need to have a control “pure water sample” so you could establish how many cycles are possible before you would need to stop.

I wonder what this would do to the RO membrane.

 

[BAD ORCA]

Are you using this to take water on-board, or to use water from your tank? If from your tank, then you will get 20-25% usable water from the amount you can store. The remaining will be tossed as waste. So for example, if you have a full 100gal tank, then you will get 20-25gal of water out of it. So you in effect have a 20-25gal tank now.

This could be OK if you are just short-sailing and don't need a lot of water between being able to fill the tank again.

Your drawing shows a storage tank, but no clear way to use that water or get it out.

One thought is to plumb the waste discharge back to the water tank. This will give you most of 100gal capacity back. It's not like this is seawater, where the brine levels would quickly escalate to the point of exceeding the system capacity. Every so often, completely empty the tank and refill. It is going to dilute anyway every time you fill the tank, so should be able to get several exchanges before complete empty.

Mark

To use water from the tank. I'm not filtering the entire tank just what i need for drinking water. The RO system will be tee'd off of the main line. It has a separate storage tank and sink faucet, so im only filtering what i drink, approx 2-3 gallons a week. Showers and dishes etc...will bypass the filter.

 

[BAD ORCA]

One thought is to plumb the waste discharge back to the water tank. This will give you most of 100gal capacity back. It's not like this is seawater, where the brine levels would quickly escalate to the point of exceeding the system capacity. Every so often, completely empty the tank and refill. It is going to dilute anyway every time you fill the tank, so should be able to get several exchanges before complete empty.

Mark

Thats an interesting idea and not at all hard to do. If this all works, it might be interesting to get three seperate water quality test after a few months of using it. One for the incoming city water. Another for the purified water and another for the waste water. If the waste water has lower contamination levels that the city water, i could see this as being a great idea. water testing labs are plentiful around here and not at all expensive.

I could also add a small tank for wastewater to use to flush the head. I have a freshwater Marine Elegance toilet.

 

[BAD ORCA]

Mark’s idea could work. It would be like washing your hands in progressively dirty water. At some point the cleaning process might be overwhelmed. It is certainly a process that could be tested. You would need to have a control “pure water sample” so you could establish how many cycles are possible before you would need to stop.

I wonder what this would do to the RO membrane.

Thats my thinking as well. I think i would need to have the water quality of the waste water checked after the filters have been in use for some time and compare against city water.

 

[BAD ORCA]

I am not familiar with water quality in LA but if it's water being produced for potable drinking water it shouldn't have constituents that are harmful. But in any case, running a RO system to remove specific species, you actually have to both design and test to be certain you are producing what you feel you need. Then the difficulty is changing feed sources. For different feed sources, you need to adapt the correct filtration to the incoming chemistry. RO filtration to remove chemicals is not as simple as plugging in a home system and getting rid of them.

What are the "nasty" chemicals you are trying to remove?

dj

agreed. I'm not looking for absolute purity, just better than what it is now. Hopefully much better.

If this all works, some months into the filtering I would have a local lab do a water quality test to see if all the hassle is worth the effort. The test is inexpensive. The filters are $100/year so this entire system needs to pay for itself in cost and hassle but mostly water quality.

 

[Don S/V ILLusion]

Are you using this to take water on-board, or to use water from your tank? If from your tank, then you will get 20-25% usable water from the amount you can store. The remaining will be tossed as waste. So for example, if you have a full 100gal tank, then you will get 20-25gal of water out of it. So you in effect have a 20-25gal tank now.

thought we clarified that. The 25% figure might apply to particularly dirty sea water but the waste amount of filtering potable water is trivial.

 

[Foswick]

My understanding of RO is that the wastewater ratio has much more to do with water pressure than water quality. But, admittedly, I only know a little bit about it.

 

[dLj]

Thats my thinking as well. I think i would need to have the water quality of the waste water checked after the filters have been in use for some time and compare against city water.

I feel you check the water chemistry of your feed water before doing the installation. Then you look to see what exactly you want to improve on and then go through how to do it. At least that's how it's done in commercial applications where a defined water quality as output is required.

dj

 

[colemj]

thought we clarified that. The 25% figure might apply to particularly dirty sea water but the waste amount of filtering potable water is trivial.

Right, I got that backwards - posting waste rate instead of recovery rate. But it still isn't trivial. 25% of the water is wasted.

Actually, this makes recirculating that waste water even less of an issue, as it doesn't concentrate much and would be continually diluted.

Mark

 

[colemj]

If the waste water has lower contamination levels that the city water

The waste water could never have lower contaminants than the water it came from.

I think the first thing you should do is have your city water tested to find out if you have the problem you think you have. It's hard to believe that a public water utility under standardized guidelines can be producing harmful drinking water. Chlorine and sulfur smells are common, but not dangerous, and easily removed with a carbon filter. If you only need 2-3 gallons of drinking water per week, it seems much easier and less space to just buy it.

Mark

 

[dLj]

Actually, this makes recirculating that waste water even less of an issue, as it doesn't concentrate much and would be continually diluted.

Mark

I'm thinking about the waste water going back into a tank. I think I'd rather just dump it. You'd slowly be making a more concentrated contaminated tank. Even though you are subsequently adding more water, it's coming from the same source and now is getting a small boost in contaminants. So the continual dilution just causes a slower increase - you would need to dump and clean the tank or it would just become a more contaminated tank over time and if the RO systems breaks down now you need that water without going through the RO.... Hmmmmm

dj

 

[colemj]

I'm thinking about the waste water going back into a tank. I think I'd rather just dump it. You'd slowly be making a more concentrated contaminated tank. Even though you are subsequently adding more water, it's coming from the same source and now is getting a small boost in contaminants. So the continual dilution just causes a slower increase - you would need to dump and clean the tank or it would just become a more contaminated tank over time and if the RO systems breaks down now you need that water without going through the RO.... Hmmmmm

dj

Yes, my original suggestion noted that the tank would need to be emptied every so often for this reason.

I doubt municipal water has enough impurities to really contribute to rapid contamination.

The OP's intent was to make a few gallons of drinking water, so doesn't sound like getting caught with a broken RO system and a contaminated tank would be more onerous than going back and getting a new tank of water.

Mark

 

[Don S/V ILLusion]

Right, I got that backwards - posting waste rate instead of recovery rate. But it still isn't trivial. 25% of the water is wasted.

Actually, this makes recirculating that waste water even less of an issue, as it doesn't concentrate much and would be continually diluted.

Mark

I wasn’t clear. Don’t know from where someone got this 25/75% split other than when treating sea water.

We’ve had an RO system onboard for close to 10 years during which I’ve seen that ratio only with sea water. Never potable water. I’d estimate a waste volume of less than 1 gallon when treating a 100 gallon volume (1%) of potable water. Often less.
Does anyone here have any practical experience to corroborate my observation or are we all debating hypotheticals?

 

[dLj]

Does anyone here have any practical experience to corroborate my observation or are we all debating hypotheticals?

The only experience i have is on a commercial scale producing strictly defined high purity water used in medical applications.

So I'd have to say pretty much hypothetical from my side in this conversation....

dj

 

[dLj]

Does anyone here have any practical experience to corroborate my observation or are we all debating hypotheticals?

@Don S/V ILLusion of course this begs the question - in the 10 years of you using this system - are you doing water chemistry tests? Do you have incoming water chemistries and the resultant RO output water chemistries? Do you have that for deciding how to run the system with whatever percentage of discharge? If so. I would absolutely love to see them.

If you don't have that. Well... You are essentially being as hypothetical as everyone else in this thread simply with the difference of running a system for 10 years without knowing what it is actually doing.

Not trying to be dismissive of what you said - simply that without actual data, in fact there exists no real knowledge - simply conjecture and "warm and fuzzy" feelings.

dj

 

[colemj]

I wasn’t clear. Don’t know from where someone got this 25/75% split other than when treating sea water.

We’ve had an RO system onboard for close to 10 years during which I’ve seen that ratio only with sea water. Never potable water. I’d estimate a waste volume of less than 1 gallon when treating a 100 gallon volume (1%) of potable water. Often less.
Does anyone here have any practical experience to corroborate my observation or are we all debating hypotheticals?

The only experience I have is from the ultra-pure RO and ion exchange units we used in the lab. The waste was a high percent of the intake, but this is definitely not making drinking water.

Otherwise, it is hypothetical and a statement gained from internet searching and manufacturer's websites.

I'm sure this is something that can be calculate with the constraints being the permeability of the membrane and the minimum pressure needed for crossflow. A pump operating at a given pressure would produce a given flow rate, and the permeability of the membrane would decide the fraction of that flow that is sent to waste.

Intuitively, 1% seems low, but I'm spitballing here.

Mark

 

[colemj]

An example of internet information is here, where a system that looks exactly like the PO's is discussed. They claim only a 20-30% recovery rate for these systems.

https://extensionpubs.unl.edu/publication/g1490/2014/html/view

And perusing RO systems for sale, one can filter the choices by recovery rate, with choices of 15, 50, and 55%.

Mark

 

[colemj]

This unit, that looks like the OP's has a 50% recovery rate.

 

[Don S/V ILLusion]

@Don S/V ILLusion of course this begs the question - in the 10 years of you using this system - are you doing water chemistry tests? Do you have incoming water chemistries and the resultant RO output water chemistries? Do you have that for deciding how to run the system with whatever percentage of discharge? If so. I would absolutely love to see them.

actually, it doesn’t answer my question but rather poses a different one. I’d still like to hear if anyone else has any actual experience.

to your question about analytical results, absolutely yes! The EPA lab in Atlanta does my analytical chemistry and bacterial/viral analyses. Quantifying waste volume is pretty simple as I am a chem engineer and lawyer (don’t hold the latter against me). Been doing this for years with other systems as well during the time in my career when I worked at EPA. While I understand your skepticism, it is misplaced.