diff --git a/discretizer/database.py b/discretizer/database.py
index 471f8acd3e73777498f7a9e9b74b7d4ecce89f2b..31ec14641611fd91ff07adf32c45811d67df5bcf 100644
--- a/discretizer/database.py
+++ b/discretizer/database.py
@@ -284,7 +284,7 @@ class TilesDatabase(BasicClass):
             _sql = f"""{_sql} WHERE ST_intersects({rectangle}, geometry);"""
 
         _results = self.connect_tiles_database(
-            _sql, user=user, password=password, host=host, database=database
+            _sql, user=user, password=password, host=host, database=database, pid=pid
         )
 
         return _results
diff --git a/discretizer/discretize.py b/discretizer/discretize.py
index 4792d12fa3a32fddd39264b1bf38e3d13fa07a96..a9a229575dd215c5d418ec9bfe3b2bdb31519ac6 100644
--- a/discretizer/discretize.py
+++ b/discretizer/discretize.py
@@ -555,9 +555,11 @@ class Discretizer(Quadtile, Config):
             )
 
         # Drop duplicate tiles from sea- and inland-water, so dissolving the combined tiles
-        # later by ID doesn't falsely sum up classification values
-        seawater_per_tile_gdf = seawater_per_tile_gdf.drop_duplicates(["id"])
-        inlandwater_per_tile_gdf = inlandwater_per_tile_gdf.drop_duplicates(["id"])
+        # later by ID doesn't falsely sum up classification values. There can be multiple
+        # spatially split water geometries in a level-18 tile (e.g. a small isthmus dividing
+        # the tile), so have to identify duplicates by geometry and not by quadkey.
+        seawater_per_tile_gdf = seawater_per_tile_gdf.drop_duplicates(["geometry"])
+        inlandwater_per_tile_gdf = inlandwater_per_tile_gdf.drop_duplicates(["geometry"])
 
         # Concatenate inland-water and sea-water tiles
         water_per_tile_gdf = seawater_per_tile_gdf.append(inlandwater_per_tile_gdf)
@@ -576,7 +578,7 @@ class Discretizer(Quadtile, Config):
         self.log.debug(f"<[{pid}]> Dissolved into {_len} water polygon geometries.")
 
         # Remove duplicate tiles from concatenation step
-        water_per_tile_gdf = water_per_tile_gdf.drop_duplicates(["id"])
+        water_per_tile_gdf = water_per_tile_gdf.drop_duplicates(["geometry"])
         water_per_tile_gdf = water_per_tile_gdf.dissolve(by="id", as_index=False)
 
         assert len(water_per_tile_gdf.index) == _len
diff --git a/discretizer/spatialfunctions.py b/discretizer/spatialfunctions.py
index e751eb62f9b5e3efa7e6beb45aa27c22ac736b10..78adab82208e4179825ec83b98187a387775b451 100644
--- a/discretizer/spatialfunctions.py
+++ b/discretizer/spatialfunctions.py
@@ -348,10 +348,13 @@ class SpatialFunctions(BasicClass):
         proj_aea = Proj("+proj=aea +lat_1={} +lat_2={}".format(miny, maxy))
 
         if isinstance(polygon, Polygon):
+            transformed_coordinates = []
             _plg = mapping(polygon)
-            lon, lat = list(zip(*_plg["coordinates"][0]))
-            x, y = proj_aea(lon, lat)
-            proj_coords = {"type": "Polygon", "coordinates": [list(zip(x, y))]}
+            for ring in _plg["coordinates"]:
+                lon, lat = list(zip(*ring))
+                x, y = proj_aea(lon, lat)
+                transformed_coordinates.append(list(zip(x, y)))
+            proj_coords = {"type": "Polygon", "coordinates": transformed_coordinates}
             area = shape(proj_coords).area
         elif isinstance(polygon, MultiPolygon):
             _plgs = [mapping(p) for p in list(polygon)]
diff --git a/discretizer/tilegrid.py b/discretizer/tilegrid.py
index 4f0da1d69583ae86de4d058c6846ae4e81cb2af7..86f6345f89f88d7c6b817d1101d8639d36f6c47f 100644
--- a/discretizer/tilegrid.py
+++ b/discretizer/tilegrid.py
@@ -54,8 +54,8 @@ class TileGrid(Quadtile):
 
         super(TileGrid, self).__init__(config, **kwargs)
 
-        # Roughly four times the length of a tile's side at level 18
-        self.buffer_size = 0.005
+        # Roughly 1 meter in degree, given a sphere with a circumference of 40000 km
+        self.buffer_size = 0.00001
 
     # FIXME Is this whole function even needed, anymore? Coastal tiles are
     # already classified in `Discretizer::static_data_in_quadkey`