I can't find the key in the sewer. I used water in a bucket and went into the sewer, but I cant find the key. Please help.

did you talk to the person who originally had the key?

 

if so you may need to examine the drain before pouring water into it, and you must RUN to the sewers to grab the key. it does disappear after time. the key is in varrock sewers right after you enter, you head west, and take the first north path, and it should appear in a pile of gunk near where mages usually train with crumble undead.

 

 

 

thats all i have to help, if nothing works, you may have forgoten somethign farther back

If you missed it, repeat the flush again.