I would give the vanda more light. I allow direct sun on my vandas. Before you try this it would be wise to talk to local growers. Your sun might be stronger than mine and have different requirements. Getting advice from your own climate generally is best. http://humanflowerproject.com/images/uploads/singaporegarden300.jpg

Link above is vandas growing in Singapore outdoors in full light...

This post was edited by shavedmonkey on Sun, Aug 24, 14 at 11:48

I think you are right. Under watered. You should shower (or soak) the roots well in the morning and then mist the plant and roots during the day to increase humidity. The flowers that are withering is normal. However, it will be difficult to re-bloom your vanda in a window sill. I grow my vandas outside under 40% shade cloth. A lot of water and a lot of light is needed to bloom vandas. However, direct noon day sunlight is too much in my area.

How well a plant can cope with full sun also depends a lot on the ambient air humidity. I remember in Madang in PNG they had hundreds of orchids growing in full sun all day, and flowering really well. But of course the humidity was very high, much the same as Singapore. That of course is outdoors, whereas your plant being indoors would be in airconditioning which makes the air a lot drier. In dry air misting is fairly temporary. If you're in an apartment then placing it out on the balcony where it gets good air circulation should work well. Generally the broader leafed Vandas prefer less sun than the terete (narrow) leafed ones. If you want to get advice from the locals, try this website, it's mostly Singaporeans who are avid gardeners.

www.greenculturesg.com/