RO water prediction

[Nemanach]

I just ordered the 75 GPD RO system with drinking water add on below from Buckeye Hydro which I will be using for brewing and drinking water. I see in Bru'n Water there is a profile for RO water but I'm assuming that the end result depends on the source.

Attached is the water report from Ward labs I got a few years ago. That is pre softener but the water will go through a softener first then the RO system. Is it possible to predict the output water profile based on this information?

https://www.buckeyehydro.com/premium-ro-systems/
https://www.buckeyehydro.com/add-on-drinking-water-kit/

 

[ScrewyBrewer]

It would depend in some degree on the total dissolved solids (TDS) of the water supplied to your new RO filter. A reverse osmosis filter will remove sodium from the feed water, and the softened water will extend the life of it's RO membrane. The RO filter reduces a percentage of the total dissolved solids in the supply water. And the lower the total dissolved solids are in the supply water the lower the total dissolved solids will be in the output water.

A good quality RO filter allows you to view the total dissolved solids in both the supply and output water. In an optimal situation your RO output water will have nearly zero alkalinity, and entering all zeros could be entered in the RO water profile.

 

[michaeltrego]

When I first installed my RO machine a few years ago, I had both my tap water and RO water tested at Ward Labs. Here were the results:

Tap pH 7.4, TDS 222, Ca 11, Mg 4, Na 46, SO4-S 5, Cl 67, Bicarb HCO3 19, Alk CaCO3 15
RO pH 7.8, TDS 26, Ca <1, Mg <1, Na 6, SO4-S <1, Cl 7, Bicarb HCO3 3, Alk CaCO3 3

I use the above RO profile in Bru'N water.
Since then, I have replaced all the sediment and carbon filter medium and cleaned the RO filter.
I brewed yesterday and the current readings for TDS are Tap 78 and RO 3.

 

[Robert65]

Get a TDS meter, about $10-15 on Amazon, and test your output. My feed water is well over 250 ppm, but my RO unit reduces it to under 5, so nothing remaining is significant. For purposes of calculations, I just treat it like distilled. By testing output TDS regularly, you'll also see when performance starts to drop off and it's time for maintenance.

 

[mabrungard]

The RO profile in Bru’n Water is from raw water with over 600 ppm TDS. It appears that your resulting water should be lower. If you have your RO water tested, you can edit the RO profile in Bru’n Water to match.

 

[Silver_Is_Money]

My budget model RO unit reduces my well waters metered TDS of 856 ppm to a metered 45 ppm. Ward Labs says my well waters TDS is 726, so my $7 TDS meter overstates Ward Labs by about 15%. Accuracy to within ~15% for $7 isn't bad. Particularly since all TDS meters (regardless of price) merely ballpark kludge TDS from waters electrical measure of current flow (conductivity).

Actual TDS measurement is a process of weighing, evaporating, and re-weighing. Ward labs likely kludges TDS by a summation of the ions process that is also only a ballpark method. Their method appears at first glance to be:

* Ballpark TDS = SUM(all present mineral ions ppm's excluding bicarb and alkalinity) + (Bicarb ppm's)/2

A typical TDS meter generally presumes ** that:
Ballpark TDS = ~0.64 x μS/Cm (MicroSiemens)

EDIT: It looks more like Ward Labs estimated TDS is derived from:
(Conductivity in units of mmho/cm) x 600

1000 μS/Cm (MicroSiemens) = 1 mmho/cm = 1 mS/Cm = 0.001 S/Cm

1 mho = 1/(1 ohm)
[ohm's are the measure of resistance to current flow, and mho is ohm spelled backwards, as it is the measure of current flow]

* NOTE: When you evaporate water roughly half of its bicarbonate ion mass escapes as CO2.

** NOTE: The constant of 0.64 is not actually a constant, and depends upon the mineral ratios within the water, and can vary from 0.5 to 0.7 (or greater). That Ward Labs presumes 0.60 here as opposed to 0.64 is an arbitrary decision on their part. The most commonly presumed and accepted median for this non-constant is 0.64.

 

[Nemanach]

I purchased a TDS meter for the rig so I can tell when the filters need replacing. What I don’t understand is how that relates to a mineral profile in the water.

Are most people sending the RO water to be tested? Do you try and calculate the minerals left based on the rejection rate of filter? Do you assume all 0s in the profile?

 

[Silver_Is_Money]

I purchased a TDS meter for the rig so I can tell when the filters need replacing. What I don’t understand is how that relates to a mineral profile in the water.

Are most people sending the RO water to be tested? Do you try and calculate the minerals left based on the rejection rate of filter? Do you assume all 0s in the profile?

If you just reduce everything by about 95% (multiply all of your individual mineral and alkalinity ppm's by 0.05) you will probably come sufficiently close to the analyticals for your RO vs. your source water. In reality a good unit will likely do even better than this. But if you soften first you will not have any calcium or magnesium and your sodium will go up accordingly (on an mEq for mEq basis).

A truly crude ballpark is that roughly half of TDS will be alkalinity (as CaCO3). At the low TDS levels of RO this should be adequate enough.