Shower walls and floor are ceramic tile and caulked around bottom. That caulk keeps getting moldy fairly fast, so I removed caulk (this is second time in a few years) and was going to replace. I noticed there is water in the gap on one wall - wicks up with a paper towel- can't see it. Does that mean there is a problem or it that normal? Walls are grouted - there are a few small areas missing grout and I was going to patch that with caulk. Could that be the source or at the drain? Wondering if I need to call a tile guy. No water on adjacent walls. The house has a crawl space foundation. I can keep trying to dry it out, but wonder if I need to address some other problem. Thanks!
Grout is porous, as are most cement-based materials. That is why tiled shower enclosures are built so that water that may (likely will) wick through the grout will hit a non-porous barrier installed behind the tile (actually, it's usually behind the substrate that the tile is installed on).
Missing grout (or missing caulk that someone mistakenly used instead of grout) should not necessarily mean that water is penetrating the waterproof membrane behind the tile substrate and damaging the underlying structure(s).
However, the age and type of the installation, the materials used, the maintenance history, the building condition, etc. could all affect this, and I have seen many showers with significant water damage to structures under the tile. You should crawl under the house and inspect the area below the shower for sign of water damage. Call a "tile guy" (i.e. a reputable licensed/bonded/insured tile contractor) if you see any issues. Otherwise, scrape out all unsound grout/caulk and let all joints thoroughly dry, then re-grout according to mfrs' instructions.
Water will definitely seep into area where the grout is missing and deteriorate the drywall behind the tiles. You need to fix that pronto and check the whole shower for missing or loose grout. Are there any tiles bulging? Hopefully there is no wall damage. Try bleach on the mildew.