RO water pH

I'm trying to learn about water adjustments and have been following the great discussions on the topic here. I only have pH strips for testing at the moment, one strip goes from 4.6 to 6.2, another that goes from 4 to 8. I'm using the new 2.0 version of the EZ Water calc spreadsheet to estimate my mash pH, making adjustments and using the strips to see if I'm in the ball park.

So today using the strips my mash was reading around 5.0. I was surprised that it came out so low. So I decided to test my source water. For this batch (2.5 gallon target) I used 2 gallons of water, with 6 quarts of that being RO water that I bought at the local grocery store. Since my mash was so low I tested the RO water with the strips and in came in around 5.0 too!

Does that make any sense? Is it normal or likely for RO water to be that acidic? If it is, then should I try to compensate for that in my mash pH calculations? Here's all the gritty details:

Recipe:
4# Marris Otter
4 oz Aromatic
4 oz Caramel 120L
2 oz Special Roast

Well water, from Ward Labs:
pH 7.5
TDS 413
Cations/Anions me/L 8.0/7.5

Na 6
K <1
Ca 90
Mg 39
Total Hardness 388
SO4-S 13
Cl 13
CO3 <1
HCO3 355
Total Alkalinity 291

I don't have a water report for the RO water, but I assume it's pretty close to 0 on everything. I know, I shouldn't assume.

Thanks!

I could be wrong, but I believe RO water is the same pH as the tap water that was used to make it. So, you'd have to get a water report on that water.

Distilled water is neutral on everything.

It will absorb CO2 from the atmosphere, acidifying it.

But don't effing worry about it. There's almost no TDS so almost no buffering.