humidity control

[swe936]

I have just completed building a wine cellar in my basement and am trying to figure a way to bring the humidity level up (now only about 20%). The cellar is passive, very well insulated, with a temp of about 59, and I'm hoping not to have to buy a system, but will if I must. The cellar holds about 400 bottles. I was told that just adding trays of water with a sponge may do it .. sounds a little off to me. Ideas would be appreciated. Thanks in advance