You have inspired me to screw around at work today.

I went through my water bills for the past year and added up all the water and sewer costs, fees, and taxes and came up with a total cost that varies between $0.0092 / gallon during high useage months (10,000 gallons - I have 4 kids) and exactly $0.01 / gallon during low useage months.

My system was advertised as having a 1.5:1 waste ratio, so I go through 2.5 gallons to make 1 gallon of water. Therefore, my high-end water cost is $0.025 / gallon.

For the reef I maintain, as I put in my last message, I can buy RC on Drs F&S for $55 and makes 167 gallons at Salinity 35, so that runs about $0.33 / gallon to mix, so my total cost is $0.355 / gallon. I don't do regular changes on that one though.

For the FOWLRs I maintain, I try to adhere to a monthly

PWC of 40 gallons, because that is one BRUTE trash can full of water. The salt I use for that is Instant Ocean Sea Salt (not RC) and that's $48 on F&S and makes 182 gallons at Salinity 32 (an extra 1/4 cup for every 5 gallons, or a total of 22 cups), so that runs $0.264 / gallon. Total

SW cost on that is then $0.289 / gallon.

So a 40g

PWC w/IO-SS currently costs me $11.56.

If I was buying water from my

LFS at $0.50 / gallon (I don't even know if any of them sell it around here), that would cost about $20, and like I said before, the salinity might not be 32 but probably 29 or 30, and you don't know if they started with

RO/

DI,

RO, or tap water for that matter.

When my

DI runs out, I am then forced to go and fill up buckets at the Culligan

RO station at Wal-Mart, which costs $0.37/gallon. With that figured into the equation, 40g of IO-SS mix runs $0.634 / gallon, or $25.36. More than

LFS, but I know what I started with and what I finised with. But, it involves a 1-hour round trip (including fill) to Wal-Mart, plus the extra hauling of buckets to the car, then into the house to mix it. So it's definitely not the deisred option.

Monthly cost:

WM

SW Mix: $25.36

LFS SW Mix: $20

Home

RO/

DI SW Mix: $11.56

Monthly Savings:

Home savings over

LFS: $8.44

Home Savings over WM: $13.8

Yearly Cost:

WM

SW Mix: $304.32

LFS SW Mix: $240

Home

RO/

DI SW Mix: $138.72

Yearly savings:

Home over

LFS: $101.28

Home over WM: $165.60

My conclusion: While purchasing an

RO/

DI system can range anywhere from $50-$400, and yearly replacement of media also varies (maybe $40-$80, maybe less), buying your own

RO/

DI system is really less about cost savings as it is about being in control of your system and eliminating all other potential variables. The time savings factor is somewhat offset, you either spend time going to the

LFS or filling up buckets, or you make your own and then buy and mix the salt.

For a

FO or

FOWLR system, buying pre-mixed

SW might be OK because you're a little less worried about the origin of the water, unless algae is a big problem and you have eliminated all other possibilities.

For a Reef system however, the cost of the

RO system and media are grossly outweighed by the cost of potentially losing all your corals during a tank crash due to any number of possible unknowns related to water origin that is out of your control. Plus, since a reef should generally be maintained at higher salinity (and Calcium, Magnesium, etc) than a

FO/

FOWLR, you really should mix up your own

SW (unless it's an all-softie tank and easy corals).

IMO, an

RO/

DI system is a must-have for a full blown reef system.