Sounds like a simple case of negligence, where you'll need to prove duty, breach, causation, and damages.
Duty: Tenant had a duty to install correct filter - a duty arises if the harm is foreseeable. You'll need to prove that the tenant knew, or should have known, that installing an incorrect filter would cause the damage that occurred.
Breach: Tenant breached his duty: You'll have to prove that the tenant actually installed the incorrect filter.
Causation: You'll have to prove that the breach of the duty caused the damages.
Damage: You'll have to prove the damages that were caused by the breach.
----------------------
WARNING: Maryland still subscribes to the doctrine of contributory negligence. If the tenant can prove that the landlord was in any way negligent, it will prevent the landlord from recovering. Even if tenant is 99 and 44/100 percent negligent, and the landlord is only 36/100 percent negligent, landlord cannot recover anything.
So, who's fridge was it? If tenant's, did LL give permission to install it and connect it to the plumbing? If LL's, did LL tell tenant what type of filter to use, and inform tenant that installing wrong filter may cause damage?