Is there cheaper or longer lasting filters that would do the job?
The RO system I just got a few months ago was about $120, with tank and faucet; because I also use it for drinking water. I plan on replacing the pre-filters every 6 months, and the membrane every 2 years. I expect to spend about $80 on 4 sets of pre-filters, and a new membrane. So I'm only looking at about $40 per year to maintain the filter. By my standards, that is pretty cheep and long lasting for what I get out of it; which is not even having to think about water quality. What can I say, I'm a lazy bastard.
There is zero waste from an r/o machine, until you throw away the "waste" water. R/O machines also work quite well with 1:1 restrictions, allowing a single gallon of garden/lawn/flowers/car-wash water for each gallon of r/o you produce.ro is great to clean heavy metals, salt (mostly), and everything else. But they produce lots of waste water and the cost of materials is high. I had one and didn't like it, so much waste.
Sounds strange, try this. Fill a clean water bottle and set it next to your plants. Does it grow bacteria? Yes, then filter or pre charge with beneficials to eat the bad stuff. If there is allot of particles that you can see as a bacterial growth or other contamination then filtering is a really good idea. But you might be able to use a conventional two part filter, because ro is great to clean heavy metals, salt (mostly), and everything else. But they produce lots of waste water and the cost of materials is high. I had one and didn't like it, so much waste.
Typically the rain will be similar to ro, not much can collect on the h2o molecules in upper atmosphere depending on where you live. Kind of a natural distillation process.
Rain is typically very low in EC, what you might be seeing is either underfeeding from the lack of macronutrients, or your ec isn't high enough for the plants liking. Do you use a measuring tool? You can see what the EC is starting out.
If the plant is wilting there could be a few reasons for that, including a bacterial growth. But you should be able to see the stuff floating in the res. What I've done for that in the past is to use maybe a drop or two of bleach per gallon then let sit overnight before using.
Take pics if you want a real eye view opinion
If that is the only water you have to work with, I think I would pursue chemically treating the water in some kind of storage tank. Then work on filtering out the particulate matter and the chlorine (or what ever oxidizer you choose) after it is 'safe' to drink. 30 ppm isn't much, it would be nice to know what makes up that 30ppm, but it shouldn't cause too much havoc, so I don't know that I would pursue RO. I'm thinking hauling water may be a better option than trying to turn that water into potable water; which in my opinion is what you need to do. If I wouldn't be willing to drink it, I don't think I would want to put it into a hydro system. Bottom line, I think this is a bit more of a task than popping a filter on, or dumping a little bleach in; and not sure it is worth it. But that is something that you would need to decide.