In general water orchids potted in bark once a week, watering till the water runs freely through the drainage holes.
This is a general rule assuming plants are potted with the right potting material (bark mixes come in different combinations and their components come in different sizes) in the right size pot.
Even so you have to take into consideration:
You are the only one who can judge your environment. If your environment is cool and damp, your plants may need less frequent watering. If your environment is warm and dry your plants may need more frequent watering.
Environments change with the seasons, especially when cold weather sets in and heating is on and when warm weather sets in and air conditioning is on. Both heating and air conditioning, when running for long periods, will considerably dry the air and cause your plants to dry faster!
Keep also in mind that plants potted in clay pots will dry faster than plants potted in plastic pots and that small pots dry faster than larger pots.
So, if you have a variety of pots (orchid clay pots, regular clay pots, plastic pots, ...) and a variety of pot sizes some of your plants may need watering every 3 days and some may need watering every two weeks.
You are the only one who can really judge when your plants need to be watered!