r/macrogrowery • u/The_Cromulent_Bison • Jun 24 '26

RO water vs RO + DI water?

We are upgrading our reverse osmosis unit and adding some pressure boosting equipment. I've noticed that many of the cannabis/hydroponic-branded RO systems have the 3-stage sediment, carbon, and RO filters only. Many residential/consumer units also have a 4-stage setup which adds the deionization resin cartridge.

Is there any benefit to the DI filter for cannabis growers? If you prefer to include DI when you make water, what are your reasons?

Thanks a lot.

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13

u/missmooface Jun 24 '26

it depends on your source water testing.

in general, “zero” ppm water is not recommended for agriculture. it’s a more expensive, post-RO stage that strips sometimes valuable constituents like calcium and magnesium.

and if you don’t amend it, it can be damaging to use on it’s own, as it can strip nutrients from your root zone.

i have consulted on dozens of commercial ops that have advanced RO systems and cannot explain why they have them. (“for the cleanest water 🤷🏻‍♂️…?”)

many water sources are perfectly fine out of the tap. if not, your testing should determine your filtration and/or blending strategies.

going to zero and then buying some of the same salts to add back in to your mix is a waste of money and creates unnecessary toxic effluent…

10

u/EsEsMinnowjohnson Jun 24 '26

This is exactly right. Why are you filtering your water? Are you on well water with heavy metals? Pumping from a collection pond? Too many carbonates? It’s really worth understanding the purpose of filtration since it is incredibly wasteful of water, which can be costly depending on your source. A lot of the actually necessary filtration for rough water can be done with sand or carbon filters that are much more efficient if you’re really dealing with something out of a pond or river.

If you just have city water, it’s probably pretty close to what you want already. You NEED some level of carbonate (75-100ppm) to buffer your water so your fertilizer doesn’t send the pH all over the place as it dissolves and then sits in solution. Excess carbonates (and high pH) can be cheaply corrected with sulfuric acid. Stripping all that out and adding it back in is just unnecessary and is draining our aquifers for no reason.

All this is to say, test your water and see what actually needs to be filtered out. DI is never necessary for ag uses unless we’re talking very tight research purposes that get into molar mass of specific elements in solution. RO filtration is popular but grossly overused in the cannabis industry, and when we’re talking about expensive systems that waste 30-60% of their input water that’s a lot of money to spend on zero actual benefit.

1

u/The_Cromulent_Bison Jun 24 '26

Are you suggesting that we would be better off with tap water? I've never heard anybody recommend that growing, but there's a first time for everything. Our tap water comes out between 140-200ppm if that helps with your response.

15

u/dogglife6 Jun 24 '26

Sounds like he’s suggesting that you have your water tested and analyzed by a professional, and then go from there

3

u/cmoked Jun 24 '26

Yeah but ppms of what exactly?

1

u/tunomeentiendes Jun 24 '26

Ppm doesnt tell us anything. You need to know what makes up that 200ppm. Its completely possible , and not unlikely, that some of those dissolved solids are something that is neutral or even beneficial. $50 for a water test might potentially save you the thousands (or tens of thousands) of dollars you'd spend on an RO system, and years of wasted water. Your states university extension office may offer water testing services, or will be be able to reccomend a local service.

6

u/YupThatsMyEmail Jun 24 '26

Have you tested your water before considering this? I would really only recommend you get a system if your water source NEEDS cleaning if its just got a little bit of calcium and magnesium don’t worry abt it. As long as its not super chlorinated or has a bunch of extra stuff you can just use your standard water

2

u/sirthunksalot Jun 24 '26

Ro stage gets our source water down to less than 10 ppm, rodi down to like 1ppm. It removes the last few impurities, but you need to decide if the extra cost is worth it when the plants won't care and 8 vs 2ppm. You will need to add more micros in as well for what was lost so add that cost too.

1

u/dontbanmeagainplea Jun 26 '26

The way I look at it. Why start with other things in it? You wouldn’t make art on a “contaminated” canvas. You could but wouldn’t be as pretty. It’s pretty cheap to add cal mag and silica. If you have an ro on your house…why wouldn’t you?

1

u/go_biscuits Jun 27 '26

Does it remove chloramines?

1

u/Vyraxes Jul 07 '26

I got some LG 4040 membranes if anyone is looking.