Hi Katie,
there are different options with the RO-systems. many of them need a reservoir and take a lot of space when installed. The PRO of this kind of systems is that you will always have water ready to be used, depending on the size of your reservoir...
There is also the direct-flow type, for which you need no reservoir, are smaller in size and can be easily placed under the kitchen sink. This is the one I have installed in my kitchen, and am very happy with it. The only COn I have found is that the water flow is quite slow, and I have to collect enought water in advance for watering the orchids (I have 80 - 90 orchids, most of them in S/H, and need 9 - 10 gallons water each time). In 3 hours I have aprox. 6 gallons collected. I have attached this link where you can see the picture of the filter I bought, as you see it is quite small 35X15X17 cm (14X6X7'')
Micro DF - Direct Flow - Ihr Spezialist für reines Wasser - Umkehrosmose und Wasserfilter aller Art
...as for personal water consume, I use it pure for cooking but mix it with some tap water for drinking (first don't like the taste of it, second it is not healthy to drink water so pure, no matter what they filter sellers say
)