If you're growing in Hydro, you'll have to get a EC/TDS/PPM and PH meter anyway - so take the EC and PH ranges of your tapwater if it's within acceptable ranges - use it.
If it isn't - buy a cheap 3 or 4 stage RO unit and use RO water mixed with tap water.
You can use Distilled water and RO water (they're much the same) but don't use them on their own without mixing in at least some tap water. They're too pure and can cause an osmotic inbalance between the roots and the rootzone which actually works in reverse - it can start osmotically moving water OUT of the roots rather than the other way round.
Don't use rainwater. Rain water can contain heavy metals and pathogenic bacteria and if left to stand for a while anaerobic harmful organisms. You shouldn't let ANY water you intend to use on your plants to stand for any length of time - it allows dissolved oxygen to evaporate out of the water and that's exactly what you don't want. Don't let water stand for any more than an hour before using it.
Water quality and quantity of dissolved salts it contains is key to the health of your plants - especially if you're growing hydroponically.
Holy CRAP!! babygro, is that for real? Yikes, man. I've been using only Walmart RO - 64 cents a gal - for my little hydro grow. Thought it was a GOOD thing. I hate being reminded what a lame ass newjack grower I am...
So, what's the story on this "osmotic imbalance"? Also, assuming ones tap water is within good range, what ratio of tap:Ro/distilled would you use?
Damn man! With all the questions I have about growing, the realization that there's a long ass list of important Q's that I don't even KNOW to ask, is truly humbling. PLEASE keep sharing your knowledge bro! PEACE
