In Soil: Use RO or Tap Water?

[BII]

If growing in soil and having the option of watering/feediing with either RO/DI or tap water (containing normal amounts of minerals/salts, aerated over night to 'dechlorinate'), which is best, recommended? Other than watching and if needed treating for Ca and/or Mg deficiencies (or simply supplementing with cal-mag), are there any downsides to using the purified RO water?

For a specific example: I just started growing in soil vs. coco, a timid first step using Happy Frog/Foxfarm soil with added 20% perlite in 7 gallon bags. Currently with a few pots now in early grow phase (~10 days old), all I've ever added to the soil has been RO water (and beneficial microbe products). At some point, should I switch to tap water (here NE US river chlorinated water with >200 ppm)?

 

[kfigerm]

get an analysis of your water source. Then you have to decide what is already in it and what to cut/supplement.
I have high cal and some N to take into account, but little mg. So i look for cal and establish the amount i want with mixing ro and tap. So one just wants to add the fertilizer and if that lacks mg in some way you can amend it with epsom salt. Thats what i do.

 

[BII]

get an analysis of your water source. Then you have to decide what is already in it and what to cut/supplement.
I have high cal and some N to take into account, but little mg. So i look for cal and establish the amount i want with mixing ro and tap. So one just wants to add the fertilizer and if that lacks mg in some way you can amend it with epsom salt. Thats what i do.

My tap water is chlorinated Potomac River (like every other Appalachian Mt. chain-draining Eastern US river tap water with good amounts of Ca an Mg) in 220-240 ppm range. Being used to using coco, of course I will compensate/supplement for Ca and Mg as needed. Until advised otherwise, I plan to continue using RO/DI water and prophylactically sometimes add calcium (as sulfate/gypsum or nitrate) and/or MgSO4/epson salt. When nutes are needed, I'll be using MegaCrop 2-part which has a good amount of Ca and Mg (In recent grows in coco, I haven't had to supplement at all).

But my real question is broader: In soil, does it matter if you use pure (RO/DI) or tap water? What are the (dis)advantages of using RO, tap or mixing in terms of improved plant productivity and quality (presuming Ca/Mg deficiencies not an issue, with suitable preventative Ca/Mg supplementation provided during the grow)?

 

[Mozzy]

Potomac River

Many years ago I lived on both sides of that river...and I read online these days that the blue catfish are out of control - invasive/nuisance, etc. and you can catch stringers of big ones just by jigging lures because there's so many . I feel bad about the impact, but wish the fishing had been as good when I lived there

...sorry for the sidebar, I'm useless on the rest since I don't grow with anything to measure ppm but curious on answers to your questions

 

[BII]

Many years ago I lived on both sides of that river...and I read online these days that the blue catfish are out of control - invasive/nuisance, etc. and you can catch stringers of big ones just by jigging lures because there's so many . I feel bad about the impact, but wish the fishing had been as good when I lived there

...sorry for the sidebar, I'm useless on the rest since I don't grow with anything to measure ppm but curious on answers to your questions

I'm not a fisherman at all. Yes, the Potomac is getting clean(er) and coming back to life slowly.

As I recall, you grow in organic soil with water only. Do you feed with RO, tap, well, or mixed water?

 

[Mozzy]

As I recall, you grow in organic soil with water only. Do you feed with RO, tap, well, or mixed water?

Correct...I only use tap water (that doesn't appear to have chromium, based on local water quality reports), but aired-out ~24-48hrs for chlorine reasons, and roughly PH’d to the mid 6s based on the periodic testing color using GH drops. No idea what ppm/ec are and no way to test.

 

[hecno]

Tape water is fine , as @Mozzy has stated chromium is the problem . I use tape water to top up my fish pond [ out door ] then use pond water for my plants .

 

[BII]

Still no one addressing my main question: Which of the water source options is best with soil, and why?

RO/DI seems the most 'natural' source of water to be added to soil (for whatever that's worth). Rain (very low ppm; essentially distilled water), not river water with its salts, is the source of nearly all surface soil water content. [I'll let my pure RO water pick up its Ca, Mg and other salts from the soil I add it to (and supplement if needed).

 

[Mozzy]

Still no one addressing my main question: Which of the water source options is best with soil, and why?

...I'll defer to any of the more knowledgeable folks on here that may chime in and can speak to feeding shit; but best will depend on what else you are doing during a grow, and what your water has in it.

For example, if you are feeding soil during a grow, then RO is a blank slate to paint with; however tap water has minerals (to varying levels which gets back to "what your tap water has in it"), so someone like me who is water-only gets benefits from the organic elements in my water (which RO wouldn't have, and neither would my plants if I used that)...such as +/? amounts of

Sodium
Calcium
Magnesium
Fluoride
Potassium
Iron
Zinc
Chloride
Copper
Phosphorus

so, mmv...

 

[BII]

With no one commenting, can I/we conclude that in soil it doesn't matter what your water source is - RO, tap, a mix, etc. - as long as the soil and/or nutrients used provide the plants with optimal levels of Ca, Mg and some other salts/minerals? Can I/we also presume that the water source has no impact on living soil, microflora, etc., something no one has mentioned?