Suede is often difficult to clean whether it be a couch or a coat. For cleaning water rings off a Suede Couch you can use a towel. Scrub the sofa with a dry towel. Dip it in a little vinegar and then scrub it again. Vinegar is usually very effective in removing all types of stains. But you must first test it on a location that doesnot show on the outside. You can also use a Suede eraser (Normally used for shoes). It gets under the suede surface and cleans out stains.
I just bought a used couch that has water stains all over it from the previous owner. The couch was in new condition (all but the water stains). I thought NO PROBLEM and brought it home. I used a cleaner I use on my clothes and household - it's called Awesome. Anyway, that did NOT work. I was very upset because this cleans everything. I remember the lady who I bought it from said her sister had the same couch and took the covers and washed them in the washer - I thought it can't be any worse than it looks now that I got ahold of it. I used a little bit of laundry detergent and the cleaner was already sprayed on it from the previous attempt. The covers turned out like new. Now I just have to figure out how to do that to the whole couch (lol).