diff --git a/src/hii_collector.py b/src/hii_collector.py
index 60dd93d..a097cda 100644
--- a/src/hii_collector.py
+++ b/src/hii_collector.py
@@ -204,13 +204,6 @@ class HiiStore:
             self.engine = None
             return False
 
-    def _pk(self) -> str:
-        if self.db_type == "sqlite":
-            return "INTEGER PRIMARY KEY AUTOINCREMENT"
-        if self.db_type == "postgresql":
-            return "BIGSERIAL PRIMARY KEY"
-        return "BIGINT AUTO_INCREMENT PRIMARY KEY"
-
     def _create_tables(self):
         from sqlalchemy import text
 
@@ -229,15 +222,16 @@ class HiiStore:
                 updated_at TIMESTAMP
             )
             """,
-            f"""
+            # Composite natural PK (no surrogate id): TimescaleDB hypertable
+            # conversion requires every unique index to include the time column.
+            """
             CREATE TABLE IF NOT EXISTS hii_rainfall (
-                id {self._pk()},
                 station_id INTEGER NOT NULL,
                 timestamp TIMESTAMP NOT NULL,
                 rain_1h NUMERIC(7,2),
                 rain_24h NUMERIC(8,2),
                 created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
-                CONSTRAINT uq_hii_rainfall UNIQUE (station_id, timestamp)
+                PRIMARY KEY (station_id, timestamp)
             )
             """,
             f"""
@@ -261,9 +255,8 @@ class HiiStore:
                 updated_at TIMESTAMP
             )
             """,
-            f"""
+            """
             CREATE TABLE IF NOT EXISTS hii_waterlevel (
-                id {self._pk()},
                 station_id INTEGER NOT NULL,
                 timestamp TIMESTAMP NOT NULL,
                 wl_msl NUMERIC(8,3),
@@ -274,7 +267,7 @@ class HiiStore:
                 situation_level INTEGER,
                 diff_wl_bank NUMERIC(8,3),
                 created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
-                CONSTRAINT uq_hii_waterlevel UNIQUE (station_id, timestamp)
+                PRIMARY KEY (station_id, timestamp)
             )
             """,
             "CREATE INDEX IF NOT EXISTS idx_hii_rainfall_ts ON hii_rainfall(timestamp)",