Please do not assume the water from your store is really RO.
I can not use my well water to brew with so I buy what was advertised as RO water at a fill your bottle station at a big store. Here is the Ad.
Our systems provide four levels of filtration: sediment filters, carbon filters, reverse osmosis and ultraviolet light. The quality of the water is terrific and it is more environmentally friendly and cheaper than buying bottled water.
Here is the test sent in to Ward Labs
Total Dissolved Solids (TDS) Est, ppm 353
Electrical Conductivity, mmho/cm 0.59
Cations / Anions, me/L 6.2 / 6.3
Sodium, Na 141
Potassium, K < 1
Calcium, Ca 1
Magnesium, Mg < 1
Total Hardness, CaCO3 3
Nitrate, NO3-N 0.1 (SAFE)
Sulfate, SO4-S 6
Chloride, Cl 58
Carbonate, CO3 6
Bicarbonate, HCO3 244
Total Alkalinity, CaCO3 211
Total Phosphorus, P 0.63
Total Iron, Fe < 0.01
"<" - Not Detected / Below Detection Limit
This is softned water not RO water. Ray Ward
I would not water my plants with that much Sodium and that much Bicarbonate will buffer most acid or salt adjustments. With all the filtering and back flushing involved with RO water are those little fill stations really RO?