RO vs Tap water

What advantages does RO eater have over Tap water?

Considering medium used in grow system some say tap water is better for coco because it contains minerals like cal mag.

I have tap water with PPM of 300, other than that tap water asks for alot more acid for PH down rather than RO.

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With RO you have to supply all the plant’s needs: 3 primary, 3 secondary, 7 trace minerals. Tap usually supplies some of this for you so there will be additional cost and attention there.

RO is tough to adjust pH because there are no Total Dissolved Solids (TDS) to buffer the change. A minuscule amount causes the pH to change dramatically.

I have two considerations for you:

  1. Get a water report to determine what Total Dissolved Solids (aka the PPM) of your tap. Having X ‘ppm’ doesn’t tell you what’s in your water.

  2. are you going to buy RO water (commonly sold as ‘purified water’ at the grocery) or are you going to install a system to filter your own? If so, cost should be considered. The cost of the unit, the install, the routine maintenance (filters can be $$), the total water used (resulting purified water + waste water), etc.


Haha didnt even have to start typing. VERY well stated @MH47 :clap:t5:


It took me a long time to find the perfect water for feeding my plants. I had trouble with my tap water at the beginning, and I had some different issues after I got an R/O system.
The PPM and pH of my tap water are both higher than average. When I started using R/O water, I would buffer it with some Cal/mag before adding the rest of the feeding. The truth is that never really worked out for me. Adding the rest of the nutrients still brought the pH down to where I always needed to raise it back up quite a bit, and my plants usually started showing problems mid flower. Then I got a suggestion to use some of my tap water as a buffer instead of cal/mag. So I bought a cheap chlorine/chloromine filter, and tried different mixes of tap and R/O. I finally nailed down a formula that works perfectly. One and a half gallons of chlorine filtered tap water in a 5 gallon jug, and then filled the rest of the way with R/O. It gives me a PPM of about 125, but more importantly, when I’m done mixing the nutrients my pH is right around 6.2, so I don’t need to raise or lower it at all.
Basically, there’s no perfect answer, but with some trial and error, you’ll find what works best for you.


I forgot to say the most important part, lol. In my experience, some tap water does a much better job than Cal/mag as a buffer!

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I don’t like wasting that much water with a RO system. A PUR Water filter does the job perfectly and almost zero waste of water. Instead of a $60 a month water bill it would be $200+ a month doing a RO system.
Oh no no no.

My PPM is a little less than yours. When I do pH, it doesn’t take a whole lot to bring it down.

Mind you our tap water is not regulated by the Texas Water Board. I don’t live in a town but I do live in a municipality and they can charge $10k per gallon of water legally if they wanted to. I know…I talked to the Texas Water Board.

So our quality of water can be semi-clear to a rust orange color.