One thing I've learned around here is that if the soil is so dry that it's pulling away from the edges of the pot, your potting mix has likely become hydrophobic, preventing your plant from getting the water it needs. I would submerge the pot in a bucket of water for a couple of hours to fully rehydrate it. You might find this link very helpful too: http://forums2.gardenweb.com/discussions/2842847/container-soils-water-movement-and-retention-xxii?n=72

For regular potting soil like Miracle Gro I usually submerge the pot until air no longer bubbles up and the pot doesn't have to be held under water. That can take 15-30 minutes, rarely more. But that's just me; I'm kind of paranoid about damaging roots by depriving them of oxygen for longer than necessary, especially if some may have dried off from dehydration.

Do you know the tricks to help drain all the excess water out of the bottom of the pot so the roots will be able to breathe? The basic method is to let the water drain out, then prop the plant up so the pot is tilted at 45 degrees (I do this in the kitchen, where I can lean the tops of tall plants against the counter or an open drawer). If the pot's drain holes are around the perimeter, much of the excess water will drain right out. If it has one hole in the middle more water will drain out when you set it upright. Repeat until no more water drains out.

Another option is to insert a wick--a strand from a non-cotton mop works great--into a drain hole and suspend the pot high enough that the wick doesn't touch the drained water until the wick stops dripping (I set the plant on top of two short pieces of 2x2 wood over a bucket, but anything like it would work).

There's a lot more, including suggestions for fast draining soil that your plant will love, in this excellent thread:

Sick or dying plants?

It depends. Treated municipal water might contain chlorine (often not the kind that dissipates after the water stands for a while), and hard water can cause harmful mineral deposits, but you can avoid that by flushing the soil frequently. Still, rainwater or R/O (reverse osmosis) water is great, especially to flush accumulated mineral deposits from soil. Just be aware that if your ficus's roots can't take up water at all, either because they've died of dehydration or from suffocation because water retentive soil stayed soggy for long periods of time, even the purest water won't help.

That being said, one of the easiest things to start with is flushing the soil to remove mineral deposits, and R/O or rainwater make that easier. I used R/O water from a supermarket machine to flush my plants, but when I'm not up to hauling stuff I use tap water from my faucet mounted filter.

Once you've done that, learned how to tell your plans actually needs water before watering, and learned how to remove as much perched water as possible after watering, you can focus on getting your ficus into a fast draining soil that doesn't pose a danger to its roots.

Another excellent thread called Dealing with water retentive soils:

http://forums2.gardenweb.com/discussions/1415041/dealing-with-water-retentive-soils?n=62