Trouble is with soaking the lens in water over night, you will still haveto clean the lens with alcohol afterwards.......
I cleaned my lenses with water to get the saw dust off a while ago, and due to the hard water in our area, you end up with smears in the delicate groves of the fresnels...
These smears are VERY noticable once projected, its aweful

Any inpurities in your water will be on the lens after the water has evaporated away
So, look online for pure alcohol or glue remover wait patiently and then clean with that....
Be careful of glue remover with any kind of ammonia in it.... it will colour the plastic the fresnel is made from.... (Even windex does this!!!)
Mostly.... Have fun, and good luck with your biuld