Hi Bertus
I use borehole water. Your TDS reading is low, no issues there (however it's not an indication of the phosphate levels). You do however need to have the water analyzed, most importantly for metals (Cu, Fe, Zn), as well as the chlorine and sulphate levels. The pH/hardness is also important (you might need to buffer the water). Magnesium levels in borehole water is sometimes elevated, also have this checked as it might cause an imbalance with calcium.
Regards