Hi,
Generally, I would cut watering back to maybe every other day. I'm not sure about your exact temperature range and what type of chids you have, but that's what I do during the winter. I grow most of my chids outside year round in CA, and I always cut back on water during the winter and cooler months, even on the vandas. The chids don't complain either.
If you have vandas, what I do is cut back on watering to every other day. Depending on how cold, I would mist the roots (ROOTS ONLY) liberally (making sure I don't get the leaves wet). Also, I basically only grow Vanda coerulea and it's hybrids, so they are more cold tolerant than other vandas, esp anything with warm parents (ie. Vanda/Euanthe sanderiana).
As for other orchids, I cut back to once a week to aobut once every other week, depending on temperature and the plant's needs.
Hope this helps, there are so many things to consider when growing orchids when it gets cold. As for watering, just remember: COLD + WET = DEAD. COLD + DRY = OK!
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