Variations in RO water?

My area water has insanely high alkalinity and hardness. My local neighborhood grocery store offers RO water through a machine that is routinely cleaned and maintained.
Testing this RO water with my Taylor test kit (for my spa) I find unmeasurable hardness, but the alkalinity is 55. Bruin'water defaults RO water alkalinity at 13. This is a significant difference in adjustments.

My question: Unlike distilled which is flat-line, is there a significant difference in RO water profiles based on the existing profile of the water running through the machine?

There could be some difference based on the input water quality, but I find that the biggest contributor to variation in the quality of RO water is the maintenance. Unless they have replaced the membrane on a regular basis, all the 'cleaning' in the world will make little difference to the water quality. Do get a TDS meter if you are going to move to RO water. That is your best check of the water quality and performance of the RO machine.

SEndorf said:

My question: Unlike distilled which is flat-line, is there a significant difference in RO water profiles based on the existing profile of the water running through the machine?

Click to expand...

Yes. If your RO system has 95% rejection for bicarbonate and the alkalinity is 100 the post treatment alkalinity will be about 5 If alkallinity rises to 200, output will go to 10, if it rises further to 300 at the input then output will go to 15. As the RO output alkalinity you observe is much higher than this then we must suppose that the rejection isn't very good. Assuming input alkalinity of 400: 1 - 55/400 = 86%. Not good at all.

I'll look into a TDS meter.
The alkalinity of my house (city) water is 350. The grocery store is 1 mile away on the same system.
But what do I do with this information? Not sure what my alternatives are. My tap water is worthless for brewing.
Maybe look for a more consistent RO supply? Where do I begin?
Thanks

SEndorf Just like any item there is a quality issue with R.O.
For basics you need to know what type of membrane they are using. If they say they are using a TFC great a TDS meter will show that.

It doesn't matter what sort of membrane they are using. As far as you the customer are concerned what matters is that the membrane is properly maintained as indicated by low TDS on a meter reading. If TDS readings are less than, say 20, everything is fine. If they get up to 100 or more either the membrane needs service or they are adding minerals back in for flavor.

AJ, I bought a TDS meter at my Brew supply and it's at 34.
Do you recommend I still follow your general guidelines in the brew science sticky?

Yes, that's low enough.

Thank you. Very helpful.
My first all grain was an English Bitter. Using bruin' water and your baseline adjustments made a fantastic winner.
Got a red ale fermenting. Hoping I'm not a one hit wonder....