No one wants to find water around (or in the tracks of) the windows in the basement, because that means there is a leak somewhere, and where there are leaks, there could be water damage and mold. If you find a contained leak that looks small, that doesn't necessarily mean you don't have a big problem — but it does increase the chances that the situation is easy to solve and that the damage might still be minimal. Once you solve the problem, take the incident as a reminder to ensure the window and surrounding wall have upgraded waterproofing.
The Weep Holes Are Clogged
Like windows in the walls of the rest of your house, the windows in your basement have small weep holes in the tracks, normally one per pane. So, if you have a sliding window with two panes, you'd look for at least two weep holes. Check that these holes are not sealed up. If the windows are close to ground level, it's possible that dirt is clogging the holes; you could also find webs or even a cover on the holes that you have to lift up. Those holes will let water drain out of the tracks.
Check along the wall under the window if you think the water actually overflowed out of the tracks into the basement. If you detect damp spots, you'll need a restoration and waterproofing company to inspect the wall.
The Window Caulking Is Cracked
If the weep holes seem fine, check around both the frame of the window and the juncture of the glass panes and the frame. Look for cracks, tracks of water on the inside of the window, and bulges that could indicate warping. The house may have settled, or the window installation may have been defective, but in either case, cracks along the window can let water in. You may need to simply recaulk around the window, but it's also possible you'll have to have the window replaced.
The Irrigation System Outside Needs Adjustment
If your irrigation system for the landscaping right outside the basement is oversaturating the soil, water could seep through walls that aren't properly waterproofed or, in some cases, pool at the edge of the window and actually enter around a pane of glass. If the weep holes are clogged, that could let water overflow into the tracks as previously mentioned. You'd need to readjust the timer on the system to water less, or you'd need to reposition part of the system, such as moving a drip-irrigation tube away from the wall of the house.
Once the leak issue is solved, have the basement checked over to ensure the waterproofing is still OK. Depending on the style of waterproofing used (in-wall barrier, coating on wall, and so on), you may need to reapply or shore up any previous methods. For more information, contact local basement waterproofing services.