Well water tends to come from limestone aquifers, and as a result, tends to be alkaline and to have moderate to high dissolved solids, which, tend to give you moderate to high total alkalinity.
Total alkalinity is a measurement of the buffer capacity for water, expressed as milligrams of calcium carbonate per liter of water. Nursery industry considers water less than 300 mg/liter as calcium carbonate useful for nursery business without requiring treatment to remove the calcium.
Surface water tends to be lower in dissolved solids. If your water comes from the Great Lakes, no treatment is necessary.
If your water comes from a river, dissolved solids tend to be low in spring and during high river flow. The total dissolved solids rises as the river flow volume decreases.
Some aquifers are in sandstone or shale, here there can be more exotic chemistry, most common iron and sulfur present. These are nutrients for plants in moderate qualities.