Question
Received an orchid as a gift. don't know the variety.  It makes large white flowers and has large, 6"+, leaves.  The flowers are slowly shriveling and falling off. Flowers come off stem at regular 1" intervals seem to alternate right and left off stem.
Is this a case of overwatering? Should I cut it back?
It was a precious gift from my son, I desperately want it to live.  It was so beautiful.

Answer
Your plant is doing just what it is programmed to do. Flowers generally open from bottom of the stem to the top and normally fall in the same order.  It is likely a phalaenopsis orchid  also called a moth orchid.  Individual flowers last 4 -6 weeks, but, of course, if you buy it in flower, there is no way to know how longm any or most of the flowers have been open when you receive it.  This is a natural process and has little to do with your watering as it is unlikely you have had it long enough to do any damage.

Having said that, there are some matters that will require you attention.  If your plant is the sort that retains its old flower spike (ie the spike stays green), you should cut it off just above the second or third node (ie joint).  Secondly, you should repot your plant after flowering using a fir bark based orchid potting mix.  Usually, the garden centers at Lowes or Home Depot carry bags of this mix.  In repotting, the pot should have lots of drainage holes and, in removing the plant from its pot prior to repotting, rinse off the roots and remove any that are mushy as these are dead.  Soak the fresh poting mix before use.  By repotting, you're helping to secure the long term health of your plant and annual flowering.