First, I'd try to find someone that has a TDS meter (Total Dissolved Solids) and check what the TDS level is in your tap water. If you can't find someone with one, you could always pick one up online for roughly $20 before s/h (check eBay if need be -- the Hanna ones are decent). It's a good idea to have one anyways, since it'll tell you when your RO and/or DI are spent / not working properly. If you don't want to buy a TDS meter and can't find anyone with one, you should be able to obtain a water quality report from the city you live in that has what it is leaving their facility (if you have city water). Granted, it's difficult to tell how much TDS is added between there and your home, but it's a number to start with.
If you have low TDS in your tap water, you could very easily go with strictly a DI unit without too many problems or frequent effort regenerating the spent DI resin beds. Otherwise, the time / effort needed to maintain a straight DI unit might not be worth it.
There is no benefit or consequence to water quality using just DI over a RO/DI unit. The RO membrane simply removes 90%+ of the impurities before they can reach the DI stage, prolonging the life of the DI resin. This is why the DI chamber on a RO/DI unit is only 10" (or smaller), while each chambers of a DI only unit are typically much larger.
If you are concerned about wastewater quantities with a RO or RO/DI unit, there are couple things you can do...
1) Be sure tap water pressure and temperature are as close to the ideal range as possible (if not stated in the info that comes with a particular unit, should be easy to locate online). Low water pressures will require a booster pump to increase efficiency. Low water temperatures are a bit more risky to play with -- if the temp gets too high, the membrane can be damaged and even melt (again, operating temp / max operating temp should be easy enough to find online). There are safe ways to help raise tap water temp, but they may not be all that effective in a basement setting. Fixing problems related to low pressure and temp will help improve efficiency, but waste to product ratio is still likely to be close to 3:1 - 4:1.
2) Look into purchasing a RO/DI unit with dual RO membranes, such as this one:
http://www.thefilterguys.biz/water_saver_ro_di.htm
There's info on that site about how it works, so I won't retype what's already there. In short, it drastically reduces the amount of wastewater being generated. While I realize this unit alone is at the top of your price range, if the cost of tap water is an issue, it could be a smart choice with the water savings alone versus a single membrane RO/DI making the added initial cost well worth it.
I use water jugs that are readily available at any sporting goods store that sells camping equipment to store / move RO/DI water. The ones I have hold 7g each and cost about $6 each. I would never attempt to pour water from them directly into any tank, especially when the jugs are full, as lifting and carefully pouring 7g up at shoulder level is just not fun for me. I mix saltwater in a 5g bucket, then pump the sw (usually after it's been stored for a week or more) into our tank with a Maxi-Jet and some vinyl tubing.
If you have low TDS in your tap water, you could very easily go with strictly a DI unit without too many problems or frequent effort regenerating the spent DI resin beds. Otherwise, the time / effort needed to maintain a straight DI unit might not be worth it.
There is no benefit or consequence to water quality using just DI over a RO/DI unit. The RO membrane simply removes 90%+ of the impurities before they can reach the DI stage, prolonging the life of the DI resin. This is why the DI chamber on a RO/DI unit is only 10" (or smaller), while each chambers of a DI only unit are typically much larger.
If you are concerned about wastewater quantities with a RO or RO/DI unit, there are couple things you can do...
1) Be sure tap water pressure and temperature are as close to the ideal range as possible (if not stated in the info that comes with a particular unit, should be easy to locate online). Low water pressures will require a booster pump to increase efficiency. Low water temperatures are a bit more risky to play with -- if the temp gets too high, the membrane can be damaged and even melt (again, operating temp / max operating temp should be easy enough to find online). There are safe ways to help raise tap water temp, but they may not be all that effective in a basement setting. Fixing problems related to low pressure and temp will help improve efficiency, but waste to product ratio is still likely to be close to 3:1 - 4:1.
2) Look into purchasing a RO/DI unit with dual RO membranes, such as this one:
http://www.thefilterguys.biz/water_saver_ro_di.htm
There's info on that site about how it works, so I won't retype what's already there. In short, it drastically reduces the amount of wastewater being generated. While I realize this unit alone is at the top of your price range, if the cost of tap water is an issue, it could be a smart choice with the water savings alone versus a single membrane RO/DI making the added initial cost well worth it.
I use water jugs that are readily available at any sporting goods store that sells camping equipment to store / move RO/DI water. The ones I have hold 7g each and cost about $6 each. I would never attempt to pour water from them directly into any tank, especially when the jugs are full, as lifting and carefully pouring 7g up at shoulder level is just not fun for me. I mix saltwater in a 5g bucket, then pump the sw (usually after it's been stored for a week or more) into our tank with a Maxi-Jet and some vinyl tubing.
