Storme, no wonder you are concerned about your vanda since there is a possibility your water carries phytophthora. Although it does not appear your vanda is suffering symptoms of this dreadful fungal disease, would it be feasible for you to purchase distilled water by the bottle to use on your orchids?
Black or brown root tips can be a symptom of toxicity which could be your fertilizer as Ray mentioned. Do you test the pH of your fertilizer water before using? There is good information regarding shriveling of vanda roots which discusses why it can be difficult to acclimate vandas at Cloud's Orchids:
Diagnosing culture problems - Pseudobulbs or Roots
However, it may be there is nothing wrong with your vanda roots or there may be problems developing as a result of all the other issues mentioned by members. Regardless, I would be concerned about the purity as well as the pH of the water you are using.
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