So if the certificate is still in one piece, try drying it out slowly. Also if you have used an agency in the past couple of years, they may have a photocopy on file which perhaps you could have a copy of - thus use the photocopy and have the dried original as backup.
Have a look at local playgroups etc as well - I worked in a playgroup up north that did morning sessions, so I was only working 9-12 (well actually more like 830-1230 with set up and pack away time). Doesn't pay amazing, but its something to do, a bit of extra money and we had school holidays off.
Or even ask at your charges nursery when you do drop off/pick up?? Even if you can be bank staff while you look for something else!