With good RO/DI system, approx long term cost per gallon?

[grwoolf]

I'm thinking about getting an RO/DI system and have been reading some threads with lots of opinions on best systems, etc., but they all seem to be very general like 'System x's filters last twice as long'. Are there any threads out there that have a comparison on ongoing cost of ownership with real numbers? I know there are a lot of variables (like the starting water quality), but I'd like a ballpark to decide if I even want to buy a system. My LFS sells RO/DI for .20/gallon which seems reasonable, but I'd like the convenience of having the water available at the house. I don't want to be spending $100 every six months to change filters, etc. when it's only costing me about $10/mth to buy the water. The up front cost doesn't bother me too much, but I don't need another thing to maintain.

[carlso63]

A lot of what will figure into your "running cost" is determined basically by how "bad" your tap water is, frankly.

I would suggest that you either purchase a TDS (Total Dissolved Solids) meter, borrow one, or have someone reputable test your water for you.

In very general terms, if you have a decently low TDS from your tap (say, under 300 ppm), you will not have to "change out $100 worth of filters every 6 months"... your filters would probably last you 12 to 18 months, or 3000 gallons of water, if you start with a decent system... your membrane (not one of the 'filters', and the most expensive part to replace, BTW) should last at least 18 months under those circumstances, IMO...

Of course, if you have a tap supply with a high TDS (perhaps as high as 700 - 800 ppm) you are going to need a more expensive unit or else you will burn through that "$100 worth of filters..."

In my case, I was able to "get away with" a 'cheap' RO / DI kit because my incoming tap TDS hovers right around 220 ppm; I am still getting "0" ppm after DI on my original filters / resin after probably 500 gal so far, in 3.5 months time of use. I paid a total of $98 for my system, including a second set of all filters & shipping, so that works out to a cost per gal (so far) of 19.6 cents / gallon - already less than what you are paying at the LFS.

If my filters all "crapped out" tomorrow - highly unlikely - and I put in my refills and got another 500 gallons before they went... that brings me down to under 10 cents a gallon...

Realistically, I am figuring on about 5 - 6 cents / gal is where I will end up, then alot lower going forward - because although I will eventually have to buy more filters, I don't have to buy the whole system again...

Hope this helps you out