A leaking window can cause severe damage to your home. Depending on how quickly you find the leak, you may be able to prevent any permanent damage. You may find water pooling on your window sill, which is usually an indication of a leak somewhere above the window sill itself. You can check the window for problems yourself before you call a builder or contractor to come out and examine the window. If you can find the problem, you can probably fix it yourself as well, which will save you money.
Check the caulking on the outside of the window frame. If you see old, cracked, or rotten caulking, you will need to replace it with new watertight caulking material.
Use a utility knife or putty knife to remove the old caulking. Slip the edge of your knife between the old caulking and the window frame. Pull upwards to eject the caulking from the joint. Pull the rest of the caulking out of the joint between the window frame and your house.
Apply silicone caulking material to the entire joint around the outside of the window. Wipe away any moisture in and around the joint before using the caulk, moisture will prevent the caulk from setting properly.
Check the where the window sill meets the jamb. The window sill and jamb (vertical frame pieces) should be sealed together. Open the window and see if there is sealant or caulk connecting the sill and jamb.
Scrape away any debris or rotten sealant between the sill and the jamb with your utility knife. Wipe the area clean with a rag. The old material might have worn away, or you might not find any sealant or caulking at all.
Squirt a layer of silicone caulking material in between the window sill and the jamb. Allow to dry before you slide the windows around.