Water Filtration System

[ToastHater]

I'm working on a plan for a DIY RV build, and I wanted to incorporate a water filtration system. Specifically, with sustainable boondocking in mind. I'd like to be able to clean any incoming water to the freshwater tank, as well as recycle gray water if possible.

From the research I've done, there are two solutions that are very similar: reverse osmosis or ultraviolet light. Both incorporate or require a pre-filter. RO requires higher pressure. UV requires a lot more power.

My understanding is that RO is the most effective, but least efficient. And that the efficiency is related to the required PSI to run it. In-home units, needing 60-70 psi or more and being less efficient. Restaurant units, needing 100 psi or more and being more efficient.

[Gray Water/Water Intake Tank]
{High PSI Pump}
{5+ Stage RO System}
[Freshwater Tank]
{Low PSI Pump}
=Out to Sink/No-Tank Water Heater=
=Sink - Out to Grey Water Tank=

Trying to keep things tight, so it isn't all over the place. I also may not be incorporating a shower within the RV, and I'll be using a composting toilet. So the only thing going into the grey water system, would be water from the sink.

I'm curious if anyone has experience with either of these systems. More specifically, how frequently do they need to be maintained/replaced?

Would you trust either, to filter grey water?

Given the available power, could they be combined together? The RO system feeding the UV system. Would this be too redundant and over the top?

[Bumpyroad]

ToastHater wrote:
What I'm getting so far is that, filtering ALL of the incoming water would be unnecessary and using an RO system to recycle water for drinking is possible (given the required power to run a pump when needed).

I'm planning on having a substantial solar system (900 Ah Battery Bank, 4000 W Inverter), so power isn't too much of a concern. Just looking at all the steps I can take, no matter how outrageous, to reduce my footprint and recycle as much as possible and increase the time I can boondock. While also keeping things compact within the RV.

I figured the pump would only need to run when refilling the freshwater tank and recycling the gray tank. Then I'd have clean freshwater on tap at all times, instead of running the pump to get fresh water. While also keeping the system clean. When boondocking, you never know how clean the water source is. Do you really want to clean dishes or yourself with that? (I guess that can be mitigated by soaps and cleaners, but still)

seems to me that you will need and aren't providing for two water tanks, one potable,one not.
bumpy

[ToastHater]

What I'm getting so far is that, filtering ALL of the incoming water would be unnecessary and using an RO system to recycle water for drinking is possible (given the required power to run a pump when needed).

I'm planning on having a substantial solar system (900 Ah Battery Bank, 4000 W Inverter), so power isn't too much of a concern. Just looking at all the steps I can take, no matter how outrageous, to reduce my footprint and recycle as much as possible and increase the time I can boondock. While also keeping things compact within the RV.

I figured the pump would only need to run when refilling the freshwater tank and recycling the gray tank. Then I'd have clean freshwater on tap at all times, instead of running the pump to get fresh water. While also keeping the system clean. When boondocking, you never know how clean the water source is. Do you really want to clean dishes or yourself with that? (I guess that can be mitigated by soaps and cleaners, but still)

[way2roll]

TechWriter wrote:




I've been running an under-the-sink RO unit for several years. While I don't boondock, the system works great. When not connected to an external water source, my RV's water pump forces water from the water tank through the RO membrane.

Which system did you go with for your RV? I usually install WATTS type systems - 7 stage, but I really don't need anything that big in our FW.

[TechWriter]

Bumpyroad wrote:

TechWriter wrote:
The main drawback of RO systems is waste water. An RO filter will "reject" a lot of water. However, I just plumb the RO waste water back into my RV's water tank.

this is feasible perhaps since you are only "treating" a small amount of water at the sink. IIRC the OP wants to treat all water, a much more difficult task.
bumpy

I addressed that . . .

TechWriter wrote:

The system I and other RVers have are under-the-sink RO units for drinking water. I've only heard from a few RVers who have "whole RV" RO systems in which ALL water going into the RV passes through an RO system. The latter is wasteful, slowwwwwwwwwww, and hardly suited to RVing, much less boondocking.

[Bumpyroad]

TechWriter wrote:
The main drawback of RO systems is waste water. An RO filter will "reject" a lot of water. However, I just plumb the RO waste water back into my RV's water tank.

this is feasible perhaps since you are only "treating" a small amount of water at the sink. IIRC the OP wants to treat all water, a much more difficult task.
bumpy

[TechWriter]

TechWriter wrote:
The main drawback of RO systems is waste water. An RO filter will "reject" a lot of water. However, I just plumb the RO waste water back into my RV's water tank.

ToastHater wrote:
That's exactly what I was thinking. I'm just not sure if that will cause more damage in the long run. Running all of the waste through the system repeatedly. Causing the maintenance/replacement cycles to be more frequent.

Bumpyroad wrote:
recirculating waste (dirty) water back into the feed water system would make that water dirtier and dirtier wouldn't it? what does that do for efficiency.
bumpy

RO 101

The system I and other RVers have are under-the-sink RO units for drinking water. I've only heard from a few RVers who have "whole RV" RO systems in which ALL water going into the RV passes through an RO system. The latter is wasteful, slowwwwwwwwwww, and hardly suited to RVing, much less boondocking.

Anyway, about RO "waste" water, also called brine. First, before water from outside your RV hits an RO filter membrane, it first goes through one or more pre-filters -- typically, a sediment and a carbon block filter.

When an RO system filters water, it lowers the TDS (Total Dissolved Solid) levels. For example, my Arizona water has these TDS levels:

724 ppm - "Fresh" water (no filtering)
697 ppm - RO waste water (brine)
24 ppm - RO treated water (the stuff you drink)

Since I plumb my RO waste water back into my water tank, the tank would eventually reach a point where the RO filter wouldn't work anymore without flushing new water into the tank.

However, if you're concerned about RO waste water fouling your water tank, just put a diverter on the waste water line: one setting to water tank, one setting to the ground or another holding tank.

I've been running an under-the-sink RO unit for several years. While I don't boondock, the system works great. When not connected to an external water source, my RV's water pump forces water from the water tank through the RO membrane.

[ksg5000]

I use RO system for my Saltwater fish tank ... IMO it's impractical for boondocking because it take a a great deal of water pressure and much of the water is discarded. Remember - when boondocking your stuck with limited energy, water supply, and waste storage capacity.

[Bumpyroad]

way2roll wrote:

Bumpyroad wrote:

way2roll wrote:
All the impurities are collected in the filter membranes themselves and stored until exhausted and then replaced. So by recycling the "waste" water in an RO system you are simply continually trying to push the same water through the system until it finally makes it. It's not any dirtier than it was to start with - it just never got polished. .

if the waste water is returned to the supply tank or source that water will keep collecting reject material and get increasingly dirty and the efficiency of the membranes will suffer.
bumpy

I think you need to read my post again. Rejected/waste RO water has not been though the system. There's no "dirt" added - it never made it into the filter.

i am assuming that the reject water is not dumped on the ground nor do you allow it to fill up your grey water tank but reintroduce it to the supply tank. that is the one problem with RO, an excessive amount of water is rejected and if not reclaimed, wasted.
bumpy

[way2roll]

Bumpyroad wrote:

way2roll wrote:
All the impurities are collected in the filter membranes themselves and stored until exhausted and then replaced. So by recycling the "waste" water in an RO system you are simply continually trying to push the same water through the system until it finally makes it. It's not any dirtier than it was to start with - it just never got polished. .

if the waste water is returned to the supply tank or source that water will keep collecting reject material and get increasingly dirty and the efficiency of the membranes will suffer.
bumpy

I think you need to read my post again. Rejected/waste RO water has not been though the system. There's no "dirt" added - it never made it into the filter.

[Bumpyroad]

way2roll wrote:
All the impurities are collected in the filter membranes themselves and stored until exhausted and then replaced. So by recycling the "waste" water in an RO system you are simply continually trying to push the same water through the system until it finally makes it. It's not any dirtier than it was to start with - it just never got polished. .

if the waste water is returned to the supply tank or source that water will keep collecting reject material and get increasingly dirty and the efficiency of the membranes will suffer.
bumpy

[way2roll]

agesilaus wrote:

Bumpyroad wrote:
recirculating waste (dirty) water back into the feed water system would make that water dirtier and dirtier wouldn't it? what does that do for efficiency.
bumpy

I was assuming that we misunderstood what he meant to say, but you are correct, it would degrade the quality of the water in the tank.

Depends on the filter. Residential RO waste water is essentially water that isn't pushed through the system. Water at a certain PSI has to pass through a series of smaller and smaller filters , down to the bacterial micron level. So from 40-60 psi you end up with a trickle of water . That's why RO's have holding tanks and they take so long to fill. There is a relief valve for water than can't pass through so it doesn't cause back pressure on the supply line. It goes down the drain. So it's not "dirty" water, it's just the original water that didn't get passed through the system. It's like using a 5 gallon bucket to fill a 12 oz glass. What doesn't fit goes all over the floor - or in the RO's case, down the drain. It's called waste because it's wasted/rejected/never made it into the system (unless recycled). It's not waste because it's dirty. All the impurities are collected in the filter membranes themselves and stored until exhausted and then replaced. So by recycling the "waste" water in an RO system you are simply continually trying to push the same water through the system until it finally makes it. It's not any dirtier than it was to start with - it just never got polished.

I'll add another caution of RO systems in general for whole house or whole RV purpose. RO filters everything - including Chlorine and Chloramine which can kill bacteria that can live in your plumbing system and holding tanks. So while you don't want to drink them and it's good to filter them from drinking water, your whole house/whole RV should not be filtered from things that inhibit bacterial growth. RO is for drinking. But there are more pros than cons to filtering an entire house/rv.

[agesilaus]

Bumpyroad wrote:
recirculating waste (dirty) water back into the feed water system would make that water dirtier and dirtier wouldn't it? what does that do for efficiency.
bumpy

I was assuming that we misunderstood what he meant to say, but you are correct, it would degrade the quality of the water in the tank.

[way2roll]

Under the sink RO systems aren't toys as previously suggested. They work and quite well in a home, under the sink, drinking water scenario. In an RV application they may not be practical. For starters they produce waste water. Depending on the quality of the unit it can be a higher than practical ratio of waste waster to drinking water. This can be recycled however but you would have to have a gravity capture and reintroduce into the system. Some RO systems use a powered pump to recycle waste waster but the energy consumption compared to the water saved is usually a wash - pardon the pun. The other challenge is pressure as you mentioned. Yet another issue is volume of water produced. Most drinking water systems are limited to about 3-6 gals over a few hours. Not practical for filling a water tank - but why would you? You really only need RO level filtered water for consumption. If just for a quick cleanup and washing dishes it's overkill. The other issue I can think of is power. An RO is going to need constant pressure to continue to produce water. That will require a water pump to run almost constantly. For that matter, any filtration system is going to require power, not just RO.

FWIW, I have installed RO systems in homes professionally for a few years. I am still working out installing a small RO system for drinking water in our RV. We don't really boondock however and I plan to incorporate cutoff switches so the pump doesn't constantly run and gravity waste water capture. Turn on as needed basically and use the waste water to clean bikes and outside stuff. My approach is really only to avoid carrying lots of bottled water which is so wasteful and has a large eco impact.

I applaud your efforts, it's an undertaking for sure.

[Bumpyroad]

recirculating waste (dirty) water back into the feed water system would make that water dirtier and dirtier wouldn't it? what does that do for efficiency.
bumpy