Watering with natural spring water?

you can, for sure... but like RO water, it likely doesn't contain some of the trace elements a plant uses -- it even uses Cl-.. but not too much of course. Now, it has a lot of that stuff.. you're going to want to convert to ppm and add to what your ferts provide and make sure it isn't too high for some of that stuff. i don't have the familiarity to tell you without converting it all,lol. nowadays, i rely on spreadsheets after setting them up once, i often forget the 'how to" part due to 1-off use. I can tell you that the primary stuff with 1ppm (mg/L - 1 ppm), is mostly nothign to worry about. It's the trace elements that you have to check.. AFter a second look, i doubt you have a problem.. just depends on any potential chemical interactions with the last couple things, lol. safe to drink, so like tap, probably isn;t too far out there with S, Ca, Mg etc. if your hydroponic feed provides this stuff in a proper amount, it will be zero worries to use this water... if it depends on tap watar providing something or being in a typical range of pH that city water tends to be in, then you need to be a bit careful or at least observe how thigns go and react immediately to a hint of deficiency in this context. if you pH your mix, you can add X mL of white distilled vinegar to ph-down safely. if you measure it and add it 1mL at a time and pH it each time you can learn how much you need to add without pH'ing it the next time.. one caveat -- consistency of your water. good city water will be in a normal range of pH and will be consistent enough to trust... not all water utulities provide such a context. so, spot checking until youknow it is consistent is wise... i don't pH anymore.. i know i add ~2.5mL to 1/2 gallon of my tap to get a good pH. My ferts get me to ~6.5 everytime on their own, so i don't have to add to that. i bought a 100pack .1-resolution pH strips. I have plenty left to use only when i see problems i can't deduce the cause of due to my recent behaviour.