Question About Making RO/DI Water

[sabien]

My unit makes 100 gpd under optimum conditions. My question, however, is how much tap water do you use (guestimate) to make 100 gallons? Anyone ever try to figure this out? My wife keeps asking me how much this hobby is going to impact our monthly expenses.

[zukihara]

I believe the ratio is roughly 4-1 so about 500 gallons total for 100g of the good stuff. Your mileage may vary however.

[Buster4900]

I agree with the 500 gallons water through the filters will give you 100 gallons of good water.

[EdKruzel]

In very poor water conditions it can be much higher.
Here in the desert our water is very hard (8.0-8.2 Ph) and during the late months we have 800x's the average community phosphate count across the country.

With an RO the average is about 2000 to every 100.

It is much cheaper to go DI only and by in bulk as well as to recharge the ions.

Ed

[sabien]

Anyone else?

[AZDesertRat]

I am not sure where EdKruzel is coming from but pH has absolutely nothing to do with hardness of water and a waste to product ratio of 20 to 1 would probably not give you sufficient pressure to make any water at all.
The average RO unit is designed to produce its rated output at 50 psi in the case of Dow Filmtec and 60 or 65 psi in the case of Applied Membranes and GE Water, 77 degrees F. and 250 to 500 incoming TDS. This is at a 4 to 1 waste to product (good) ratio.
So as others have pointed out uou use 500 gallons to produce 100 gallons of good under normal conditions, if you water temp is colder or hotter or your presure is different it will vary a little.

[EdKruzel]

So Az, you say that alkalinity and hardness have no correlation?

I don't pretest to know all about RO/DI units, but I welcome you to travel a few hours east and give it a try here.

Ed

[AZDesertRat]

A pH of 8 to 8.2 is fairly normal. What you are referring to as hardness is actually alkalinity, kh or carbonate hardness and not true hardness which refers to calcium and magnesium.

http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html

I have never heard of a RO with a waste ratio of 20:1, do you really waste that much and if so why? Our water is from both the Colorado River and the Salt River and is both extremely hard and high in TDS but no one wastes that high around here including commercial and municipal systems.

[MOX]

well i am runing my ro on a well and i get crap for psi its around 30-50 psi and i am told that in a city house the psi is on avarage of 70-90 so i am only geting about 10 gpd on a unit made for 100 gpd but back on subject before i drilled into a waste line i had it in a 5 gallon buket and lets just say it made a mess in the basement but as far as i could tell i am betting that the 4 to 1 is right on the money

but the more psi u have the more good ro u will get and the more waste u will also get so if any one could tell me what the happy midd range is ill be greatfull

[EdKruzel]

I switched to buying my water prefiltered to save money.
I tried the Tap Water Filter (http://www.marinedepot.com/aquarium_reverse-osmosis_aquarium_pharmaceuticals.asp?CartId=) and averaged 2-5 gallons on three cartridges before the resin was spent.

I am considering going with a commercial deionizer since I moved to the west end of town where we fall under another pumping station/plant and the water (while still very bad, you should see my shower!) is a bit better.
No waste and I'll be able to recharge the resin.

Ed

[crumbletop]

Sabien,

I'm new to this too, so my calculations may be all out of whack, but here is what I put together in order to see if I could afford the monthly upkeep. I believe this is very conservative because the heater won't run 24x7, and I doubt I'll routinely use the amount of water I listed. I also will likely not be running my lights for the length of time listed. I got the water and electric prices from my local companies...

Electric rate this is based on is $0.07086 per Kilowatt Hour (kwh).
Water/sewer rate this is based on is $4.07 per 1000 gallons.


Electricty:
Lights x 14 hours per day (360 watts) = 5.04 kwh per day.
Pumps x 24 hours per day (42 watts) = 1.008 kwh per day.
Skimmer x 10 hours per day (20 watts) = 0.2 kwh per day.
Heater x 24 hours (200 watts) = 4.8 kwh per day.
Total = 11.048 kwh per day x 30 days = 331.44 kwh per month.
Electric Cost per month = $23.49 (331.44 kwh x $0.07086/kwh)

Water:
Water at 100 gallons per month (RO/DI water) at 1 gallon out for every 5 gallons in = 500 gallons/month total used.
Water/sewer Cost per month = $4.08 (500 gallons of water in = $2.04 + 500 gallons of sewer = $2.04).

Total cost per month = $27.57

Also, Reefcentral has an electricity calculator that you can try out:
http://www.reefcentral.com/calc/tank_elec_calc.php