I'm sure that this is NOT an issue, or I would have heard about it, but something I was thinking about this weekend has me confused.

When pouring a foundation (ICF or not), you first pour footings, then walls, then the floor, correct?

When doing an ICF wall, is the concrete of the floor poured up against the foam insulation on the inside of the wall?  In my mind, it doesn't seem like that would create a good "seal" between the wall & the floor.  I'm assuming that there's something I'm missing, that would ensure that an ICF basement is water-tight.

So many ways to do it...

1. Pour the slab on top of the footing strip but against the foam... this would seal it off if done properly.
2. pour the slab against the foam. Structurally adequate but not a good seal
3. pour the slab against the concrete of the wall - you would have to remove the foam about 3 or 4" high around the whlole project... you would have rebar sticking out.... - use a sealant...
4. pour the slab and footing strip at the same time...

Typically, pouring against the ICF or any foundation wall is not an issue. The seal/waterproofing is taken care of on the exterior of the wall. Making sure the bottom of the wall at the wall/footing junction is waterproof on the outside is the key and you might even consider a very slight slope on the top of the footing away from the wall, so that any water that collects at the bottom of the wall drains away over the top of the footing and into the drainage tile. Pouring the floor on top of the footing and against the wall also provides added protection since the water needs to rise the thickness of the slab on both sides for water to reach the floor level. This is not accounting for capillary action.

This is pretty much what I assumed, but I was curious.  Thanks to both for the replies!!

Use Certainteeds Form- A Drain which will relieve the hydrostatic pressure and water won't rise from below unless you you have a greater source of water than the system can handle. ( Which is a lot of water ) Will also vent radon.

http://www.certainteed.com/products/foundations/foundation-insulation/311520

I'm doing it a little different in that I'm pouring the footings (done), pouring the basement slab (in progress), then stacking and pouring the ICF walls on top of the footing just outside the basement slab.

Regardless of which way it is done, the slab to wall joint is not intended to be waterproof. Exterior basement waterproofing on an ICF needs to be applied on the outside foam and over the top of the footing. An exterior footing drain system then drains the water away. In theory, water should never get to the concrete in the ICF wall. Any water under the basement slab should be handled with a similar drainage system around the inside of the footings just under the slab (I'm using 4" PVC perforated pipe and gravel).

I have a walkout basement on the side of a hill, so it is easy for me to run the inside and outside footing drains separately to daylight. The inside drain requires one or more sleeves through or under the footing.

If you don't have a walkout basement, you will likely have to have sump pumps to pump out the accumulated water. I wouldn't connect the inner footing drains to the outer footing drains or sumps - you don't want water from outside the footing flooding under the slab via the drain/sump system.

See the light green pipe in the photo below.  That is my inside footing drain system under the slab.   I have penetrations under the footings at the near corner and far corner to allow the water under the slab (if any) to drain down the hill.  With the 3/4" gravel and perforated pipe under the slab along with a 10 mil vapor barrier that will extend over the inside of the footing, water should not build up under the slab to create any leaks in the basement.  I also have a "T" in the drain pipe visible on the left side of the photo that will be vented to atmosphere in case any gases or radon were to buildup (not really likely since I'm building on solid red clay).

You can also see my basement slab forms on the footing.  These are 5" tall to allow for 1" of XPS under the 4" slab.  I'm in central Arkansas where deep earth temps are ~60F so I figured 1" of XPS was enough just to create a thermal break (insulation under slabs is rarely done here).

Arkie's system is pretty much the same as I have used, with good results, for many years.
As to the general question of floor/wall joints, this condiition exists with any type of construction. This 'cold joint' is the entryway for a lot of basement water problems. The bottom line is that this joint exists and can be the source of leakage. The only true solution is to provide interior footer drainage with clean rock or some other form of drainage plain under the slab, to relieve the hydrostatic pressure. You cannot rely on exterior drainage systems to stop the ground water pressure that causes this type of leakage, especially in high clay soils.