Water once a week in winter. Tap water is O-K to use but it causes salts to accumulate in the soil. Cymbidiums are very sensitive to salts in the soil. Heavy watering helps flush these salts out. I like to use bottled water on my orchids.
Bottled water tends to contains fewer impurities.
With all that watering, its no surprise to know that Cymbidiums need frequent fertilizing. Choose a good water-soluble orchid fertilizer and apply while watering once or twice per month. Its nice to know Cymbidiums are usually pest-free. However, on occasion, you'll find scale, spider mites, and aphids on the leaves or flower stalks. Commercially available pesticides work just fine as long as you follow package directions.