Without some kind of cleaner, water may not be enough. A film of grime and dust can remain.
I take my ficus tree out on deck, spray it liberally with a safe cleaner. (Last time I used ammonia-free Glass Plus, mixed half&half with water) and then spray with the hose or a spray bottle of clean warm water.
It came out spotless. Beautiful and green. No dust film at all.
Just drip dry, shake off the excess water. voil'a.
Smaller plants can be done in the sink, tub, or shower.