RO vs tap water

[triggerfish55]

i was doing some research regarding my municipal tap water, and i found the fact sheet indicating the concentrations of all elements , and organic compounds in the tap water. here are some of the important values

alkalinity 90 mg/l
calcium 35 mg/l
ph 7.7
copper , lead negligible
iron 0
magnesium 9 mg/l
nitrate 0.43mg/l
nitrite negligible
silica 1.5mg/l
strontium 0.18mg/l

all other potentially questionable or harmful substances are either extremely negligible or at zero

so my question is what is the point of RO water, i always hear people saying that tap water has all kinds of bad stuff in it but the data shows that is incorrect, in fact this tap water contains things like calcium and magnesium that i would dose anyway. i haven't dosed calcium in almost a year but yet my calcium levels are at 430, this was always somewhat mysterious to me and now i am starting to think that it is due to the small amounts of calcium that gets added to every top off i do.
also from what i understand RO water has a very low PH, which i imagine is a bad thing.
disclaimer this is just the case for my municipality, i'm not saying that this applies for every city or region

[madchemist04]

the main reason to use ro water is to limit the introduction of nutrents like phosphate, the ph of ro water is not important, since many of the compounds that effect the ph are in low concentrations, the ph tends to be low due to the carbon dioxide in the air.

[E Rosewater]

Some people have luck with tap water, myself included. I ran tap for over a year without issue.

That being said you will not find many people who will suggest using tap for many reasons. The unknown is the reason I use RO/DI now.

Negligible copper or zinc for human consumption can kill inverts at coral. Copper can start being lethal not much over 10ppb, your municipal water supplier isn't going to test to that level.

Adding water that contains nitrates or phosphates, especially in you top off will begin to concentrate these and can lead to serious algae/dino/cyano problems and potential coral death.

Adding silicates can lead diatoms.

That level of alkalinity is 5dkh which means if you use a salt that's 10 dKh you'll have water that's 15 which is very high. Also as you top off it will increase those levels.

RO/DI has a pH of 7. Which is low but it doesn't matter because it has no buffering capability. The alkalinity which we keep our salt water has a very high buffering capability, this means adding the levels of fresh water that we do to our tanks has no pH effect.

[Paul B]

I used New York City water for years with no problem, then I moved to Long Island and I also used tap water for years until one day my town added zinc orthophosphate to the water supply to prevent corrosion in the pipes. I lost all my corals in an hour. That happened to me 3 times. But besides that, it is fine.

[ska d]

Why don't you try using it and see what happens , it may be fine. But how are you going to know if the water company decides to add something. Is it worth losing everting to save a few buck on ro.

[bertoni]

As people have pointed out, tap water has some risk associated with it. What the odds of having a problem are unknown, but RO/DI seems like a cheap safety net to me, personally.

[Fishyoga]

My city puts out a monthly water quality report each month, that details 30 different substances.
For January (just a sample):
Copper 2mg/L
Aluminum 10mg/L
Mercury, Manganese, Lead 2mg/L

I don't know what this corresponds to in ppm or ppb, bu I agree with the thoughts that say very small amounts will be harmful to certain aquatics before a human would even notice anything.

[bertoni]

Copper at 2 mg/L would be lethal to a wide variety of animals. Aluminum isn't good, either. With the mercury in it, I'm not sure I'd drink it myself.

[disc1]

Alkalinity at 90ppm may push your alkalinity up in your tank depending on how fast you use it and how much top off water you use.

[disc1]

Originally Posted by triggerfish55

also from what i understand RO water has a very low PH, which i imagine is a bad thing.

But it has zero alkalinity and zero buffering capacity so its pH doesn't mean squat.

[E Rosewater]

mg/L is ppm, or 1000ppb

[triggerfish55]

Originally Posted by disc1

Alkalinity at 90ppm may push your alkalinity up in your tank depending on how fast you use it and how much top off water you use.

interestingly enough my alkalinity is kind of on the low side, its the only thing i have to actively dose to keep in balance. but i think that is because it gets used up fast. however when i make a new batch of salt water the alk is usually on the high side.

my municipality tests over 300 different elements and substances, ive been using this water in my reef for 3 years, with great results.
copper is found in natural seawater at concentrations of ~0.001 to 0.01 mg/L. and the tap water fact sheet shows consistent copper concentrations of 0.001-0.002 over the last 10 years of testing. which means the copper levels are at or below what is found in nature,

[E Rosewater]

Not all copper is created equal. There are huge differences between the toxicity of organic and inorganic copper.

Also they are not taking their water samples for your tap.

Not trying to talk you into anything but it only takes one bad day in the water supply.

[triggerfish55]

Originally Posted by E Rosewater

Not all copper is created equal. There are huge differences between the toxicity of organic and inorganic copper.

Also they are not taking their water samples for your tap.

Not trying to talk you into anything but it only takes one bad day in the water supply.

so what would be examples of organic copper ?

[E Rosewater]

They would likely be copper bound to a form of organic ligand. As explained in the abstract of this article 60-90% of copper in the sea is organically bound.

http://www.researchgate.net/publicat...ds_in_seawater

[crissie]

The tap water where I live is pretty good, it's probably perfectly safe to use, however I like the security of using RO water. It gives me the reassurance that, should thing inexplicably go belly up, it wasn't down to me being a bit lazy (not saying using tap water is lazy, just that this is how I think I would feel).

[bertoni]

It's true that a lot of the copper might be bound to organics, but that's still a lot of copper. If it were bound up well enough, it might be safe, though.