diff --git a/rust/src/main.rs b/rust/src/main.rs
index 9e462fa..ff83ff3 100644
--- a/rust/src/main.rs
+++ b/rust/src/main.rs
@@ -127,6 +127,7 @@ struct PlantState {
 }
 
 #[derive(Serialize, Deserialize, Debug, PartialEq)]
+/// humidity sensor error
 enum SensorError {
     Unknown,
     ShortCircuit { hz: f32, max: f32 },
@@ -134,13 +135,23 @@ enum SensorError {
 }
 
 #[derive(Debug, PartialEq, Default)]
+/// State data for water tank
+///
+/// TODO unify with TankStateMQTT
 struct TankState {
+    /// is there enough water in the tank
     enough_water: bool,
+    /// warning that water needs to be refilled soon
     warn_level: bool,
+    /// estimation how many ml are still in tank
     left_ml: u32,
+    /// if there is was an issue with the water level sensor
+    /// TODO merge with left_ml as Result<u32, error_type>
     sensor_error: bool,
+    /// raw water sensor value
     raw: u16,
 }
+
 #[derive(Serialize)]
 struct TankStateMQTT {
     enough_water: bool,