Science!Greenhse effect.

Greenhouse effect is caused by gases in Earth's atmosphere absorbing and emitting infrared radiation. If a large amount of greenhouse gases are presented, it will warm up the Earth just like putting a blanket around us.

Water vapor has very good absorption properties towards infra-red radiation. In conjunction with its large presents in Earth's atmosphere, it is the largest contributor to greenhouse effect on Earth.

For water vapor absorption diagram:
http://en.wikipedia.org/wiki/Water_absorption
As you can see, water vapor does have good absorption rate at the infrared range.

For greenhouse gases comparison:
http://en.wikipedia.org/wiki/Greenhouse_effect
In this article, water vapor ranks the top as it is abundant in atmosphere.

Since Singapore is near the Equator, it has a topic climate. It is, in general, hot, humid, plenty of rainfall and lots of typhoons/monsoons.

We normally don't regard water vapor as a greenhouse gas because it is naturally occurring in the air.
However water vapour may trap many particulate matters and dissolve acidic gaseous pollutants, giving rise to photochemical smog.
in this sense you may "treat" water vapor as a greenhouse gas in a loose sense.