SWOT is designed so that the signal that it sends bounces off the surface of liquid water, like the top of a lake, a reservoir, a river, a wetland, or an ocean, and eventually returns to the satellite. That same signal does not reflect off of land or ice.

What this means is that the information that comes back to the satellite is about liquid water that we can see on Earth's surface. For liquid water that is underground (groundwater), we have another mission called the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. GRACE-FO measures gravity changes on Earth, and because water is so heavy, we can observe any changes in groundwater using those gravity measurements.

For solid water that is on top of the surface (ice caps), we have another mission called Ice, Cloud and land Elevation Satellite (ICESat-2). -CD