How can I stop river from leak into my house close at hand my deck? I own a proporty that is a split even with the...

I own a proporty that is a split even with the lower even being to some extent underground. We rent this place out to our friends and they recently told us that the ceiling within the bedroom in the lower smooth is showing water stains and be a little drizzly to the touch the other day. The spots are showing up close at hand the patio door that lead to the deck upstairs so I think the problem lies contained by that area. What could be the problem? We haven't replaced the door just now, but its not an old door. How could I fix this or who would I contact to carry more information about fixing this? I don't know where on earth to start!!
Answers:    I recently replaced a sliding cup door for a friend, some of the wood under the door have rotted. It seems similar to the door channels hose down to its base. As a makeshift fix to protect your investment I would thoroughly caulk the bottom of the door. Then get surrounded by touch with a right carpenter to have a problem checked out.
You may be capable of caulk the area around the balcony door and especially the sill. If there isn't a gutter above the deck I would take one. Water can seep within any cracks in the siding from wet splashing back from the deck.