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Thread: Filter for top off water

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    Filter for top off water

    My house RO filter makes beautiful completely neutral TDS free water at the cost of a lot of backwash water and time. Is there a good filter that will do something similar on a larger scale for water used to replace evaporation in the pool? It seems like I get my TA just right just to have it go right back up after a few replacement fills. For folks with CH issues and scaling it might be useful too.
    Intex 16'x32'x54" 17Kgal AGP since 2014. Sand filter, Hayward skimmer, home built 10'x15' deck and stairs, solar heater. High TA tap water, moderate rainfall, weekly use. Treated with 10% bleach, MA and some dichlor initially. Soon to add borates.
    Taylor K2006C
    Future projects - automatic chlorine pump, online pool sensors, better heater, IGP (maybe)

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    JoyfulNoise's Avatar
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    Re: Filter for top off water

    Quote Originally Posted by welbo View Post
    My house RO filter makes beautiful completely neutral TDS free water at the cost of a lot of backwash water and time. Is there a good filter that will do something similar on a larger scale for water used to replace evaporation in the pool? It seems like I get my TA just right just to have it go right back up after a few replacement fills. For folks with CH issues and scaling it might be useful too.
    Not really. As you know, the household RO systems waste A LOT of water (I think I've seen systems that require 4 gallons of input water to create 1 gallon of RO water). Commercial grade systems require very high pressure pumps with several cascading RO membranes as well as pre-filtering to remove sediment and chlorine. Those systems are huge in comparison to household RO systems but can achieve 85-90% efficiency in terms of waste water generation.

    The only other filtration systems you will sometimes find on pool fill lines are salt-based water softeners to remove calcium and/or iron removal systems for well water. But even then, you can only use those systems for minimal top-off or else they will regenerate endlessly and waste a lot of water.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Re: Filter for top off water

    I don't have to have perfectly clean water. My main motivation is to filter out the alkylines so my TA doesn't go up with every fill. Those with metals or calcium might need a different type of filter. If there is no such thing, I know some people who could probably invent it. Maybe we can sell them at tftestkits.com and all get rich!
    Intex 16'x32'x54" 17Kgal AGP since 2014. Sand filter, Hayward skimmer, home built 10'x15' deck and stairs, solar heater. High TA tap water, moderate rainfall, weekly use. Treated with 10% bleach, MA and some dichlor initially. Soon to add borates.
    Taylor K2006C
    Future projects - automatic chlorine pump, online pool sensors, better heater, IGP (maybe)

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    Re: Filter for top off water

    Quote Originally Posted by JoyfulNoise View Post
    Not really. As you know, the household RO systems waste A LOT of water (I think I've seen systems that require 4 gallons of input water to create 1 gallon of RO water).
    Adding a permeate pump to a household system improves it's efficiency and recovery speed.
    8.5k gallon IG pebble sheen play pool with Intellitouch control, Intellifo VF, IC 20, Rainbow tab feeder (not currently in use), Pentaire mystery cartridge filter with labels faded to the point I have no idea on the model, Intellibrite 5g LED light, Hayward Navigator. Adding IntelliPh and Crestron control next.

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    JoyfulNoise's Avatar
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    Re: Filter for top off water

    Quote Originally Posted by dtlight View Post
    Adding a permeate pump to a household system improves it's efficiency and recovery speed.
    Thanks for that info. Good to know if ever I install an RO system. Even with the improved performance, a 35 GPD RO system won't cut it. Most average sized pools lose more than that per day.

    I suppose one could pay for a water company to come in and give options/quotes for a system. You'd want something that is able to replace about a 1/4" of water per day in a pool. So based on your pool surface area, you'll have to figure that out. I live in the desert so evaporative loss is huge for me in the dry months. 1" of water in my pool is almost 300 gallons, so I would guess an efficient RO system to replace that much water would be pretty big and need to use some higher pressure pumps.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    JoyfulNoise's Avatar
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    Re: Filter for top off water

    A good resource for home RO information is US Water Systems, the same folks we recommend for Stenner pumps.

    Just to put some numbers on it - for a whole house RO system, you might get something like a 4,000 GPD RO setup. An RO system is typically spec'd to deliver 50% of the stated flow rate, so a system like that would theoretically deliver 2,000GPD. The base price for a system like that is currently listed around $8,000 not including installation costs. For municipal water like mine, I'd also need to add an active carbon backwashing pre filter to remove chlorine, chloramines, etc., as well as an anti-scale injection system (basically looks exactly like a chlorine stenner pump setup except it uses an anti-scale chemical). Finally, I would also likely need to do post-treatment calcite filter to raise CH and pH in order to not cause corrosion of pipes inside the home (it's not a good idea to have huge differences in mineral ion levels and pH between water in a pipe and water outside a pipe; it leads to galvanic corrosion). The addition of the pre- & post-treatment equipment would add about another $2,000 to the setup. One would also have to factor in the on-going costs of running the unit which include a variable-speed pump to send re-pressurized water back into the house plumbing, particle/sediment filter changes, anti-scale and calcite raw chemicals as well as any worn out Stenner tubes and UV disinfection lamps (the final stage of the RO injection is to run it through a UV lamp before going into the household plumbing to destroy viruses that may have made it through). One would also have to include (especially where I live as water is not cheap) the cost of all the waste water generated. For 2,000 gal system, one would have to assume that at least 15% of that value was generated in waste water, so something like 300+ gallons of water or 0.5CCF per day. If I'm operating at my peak water usage time where I hit the Tier 3 water charges, an extra 1/2 CCF per day is almost $4 to $6 per day added to my water bill.

    One could theoretically tap off some of the water from before the final calcite filter to use an external water source. But you definitely want to limit usage in the pool as the system will only provide, at best, 2,000 gallons of water for all the days needs. The installation would cost about $10,000 worth of equipment and likely a few thousand dollars more for professional installation. While you would get a whole-house RO system out of the deal, I'm not sure it's worth the huge up-front cost unless you live in an area of the country where raw supply water is cheap.

    See here for details - US Water Heavy Duty Whole House Reverse Osmosis System
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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