The Collaborative International Dictionary of English v.0.48:

Seepage \Seep"age\, or Sipage \Sip"age\, n.
   Water that seeped or oozed through a porous soil. [Scot. & U.
   S.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Seepage \Seep"age\, n.
   1. The act or process of seeping; percolation.
      [Webster 1913 Suppl.]

   2. a fluid that seeps out of a container; as, seepage from a
      reservoir.
      [PJC] Seepy

WordNet (r) 3.0 (2006):

seepage
    n 1: the process of seeping [syn: seepage, ooze, oozing]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "seepage":
   absorbency, absorbent, absorption, access, admission, adsorbent,
   adsorption, assimilation, blotter, blotting, blotting paper,
   chemisorption, chemosorption, condensation, digestion,
   distillation, dribble, drip, dripping, drop, effusion, endosmosis,
   engrossment, entrance, entree, entry, excretion, exfiltration,
   exosmosis, extravasation, exudation, filtering, filtration, import,
   importation, importing, income, incoming, infiltration, ingoing,
   ingress, ingression, input, insertion, insinuation, intake,
   interpenetration, introduction, introgression, intrusion, leaching,
   leakage, lixiviation, ooze, oozing, osmosis, penetration,
   percolating, percolation, reception, seep, seeping, sorption,
   sponge, sponging, spurtle, straining, sweating, transudation,
   trickle, tricklet, weep, weeping