Personally, I wouldn't trust bottled "spring" water. You can also buy 1 gallon jugs of "distilled water" for less than a $1 in most grocery stores, which would ALSO be far better than trusting the "spring" water. Another option would be "purified drinking water" as it will be far more reliable and less bacteria laden than the spring water. The spring water could also be far harder than your current water, adding a whole other complication. When adding, take your time, as the new water will have a FAR different chemistry than the current water, and the animals will require time to acclimate to the new water.
With the nitrates "off the charts" the water change should be as large as possible. So, for less than $5, you should be able to refill the tank with distilled water and have virtually no nitrates, at all.