How WFP (Water Fed Poles) works
A Glass Cleaner can use an extended pole ether in sections or extend telescopically. There are various sizes ranging from 4' to 80' and even higher.
Pure water is pumped up through hose and passes through jets. The jets spray low pressure pure water. The dirt is loosened by scrubbing the glass. The window is now clean from the final rinse with pure water.

Pure Water!
That means no harmful chemicals. Water is purified onsite or offsite. This purification process removes all the total dissolved solids.
There is no minerals in the water now so when it dries on the glass it dries perfectly clean since the pure water actually attracts the dirt off the glass.

How about just hosing them off?
Water naturally has many types of dissolved solids. Look at the bottom of your shower after awhile of not cleaning it, same thing.