Use a washable or waterproof cover over your crib mattress to protect the mattress and wipe down the crib mattress or spot clean with soap and water after leaks occur. (mattresshelp.org)
A hybrid diaper is also an easy option... some form of waterproof cover that you switch out the inserts in... only changing the cover out when it gets dirty.. (celebritybabies.people.com)
Babies are in waterproof covers so often that it's nice to give their skin a chance to breath and this can also help with diaper rash. (mygreennest.com)