Most cost effective way to get water? (GB)

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It depends on how you want to fertilize. You can water orchids with the pure water, nothing added. You will need to fertilize. Some people use a very low concentration of fertilizer at every watering. Others fertilize once a week or once a month, with somewhat higher concentrations.

I suggest you read and learn about fertilizing in the Free Information section of the First Rays Web site. Ray is an OB member and posts frequently.