diff --git a/ui/src/api/CWaterPumpAPI.js b/ui/src/api/CWaterPumpAPI.js
index 978eb55..2942d15 100644
--- a/ui/src/api/CWaterPumpAPI.js
+++ b/ui/src/api/CWaterPumpAPI.js
@@ -10,6 +10,39 @@ function preprocessApiHost(apiHost) {
   return url;
 }
 
+function preprocessResponse(response) {
+  if(null == response) return null;
+  if('error' in response) {
+    // TODO: handle errors in slice/SystemStatus.js
+    throw new Error(response.error);
+  }
+  // normal response
+  // convert "water threshold" to "waterThreshold"
+  response.waterThreshold = response["water threshold"];
+  delete response["water threshold"];
+
+  // convert "time left" to "timeLeft"
+  response.pump.timeLeft = response.pump["time left"];
+  delete response.pump["time left"];
+
+  // add field "updated"
+  response.updated = Date.now();
+  // difference between current time on client and time on device
+  response.timeDelta = response.updated - response.time;
+  return response;
+}
+
+// TODO: probably we need to know "ping" time to sync time more accurately
+// Example:
+//    00:00.000 - client sends request
+//    00:00.100 - server receives request and set 'time' to 00:00.100, timeLeft = 1000ms
+//    00:00.200 - server sends response
+//    00:00.300 - client receives response, but 'time' is 00:00.100 and timeLeft = 1000ms
+// total time: 300ms
+// on average, time to one-way trip is 150ms
+// so, we adjust time by 150ms i.e. time = 00:00.250, timeLeft = 850ms
+// in this case, error is 50ms (150ms - actual 00:00.100), instead of 200ms (300ms - actual 00:00.100)
+//////////////////////////////////////////////////////////////////////
 class CWaterPumpAPI {
   constructor({ client=null, URL }) {
     this._client = client || axios.create({ baseURL: preprocessApiHost(URL) });
@@ -19,17 +52,17 @@ class CWaterPumpAPI {
     const response = await this._client.get('/pour_tea', {
       milliseconds: runTimeMs,
     });
-    return response.data;
+    return preprocessResponse(response.data);
   }
 
   async stop() {
     const response = await this._client.get('/stop');
-    return response.data;
+    return preprocessResponse(response.data);
   }
 
   async status() {
     const response = await this._client.get('/status');
-    return response.data;
+    return preprocessResponse(response.data);
   }
 }
 
diff --git a/ui/src/store/slices/SystemStatus.js b/ui/src/store/slices/SystemStatus.js
index 8abba9f..4910334 100644
--- a/ui/src/store/slices/SystemStatus.js
+++ b/ui/src/store/slices/SystemStatus.js
@@ -1,25 +1,9 @@
 import { createSlice, createAsyncThunk } from '@reduxjs/toolkit';
 
-function preprocessSystemStatus(systemStatus) {
-  if(null == systemStatus) return null;
-  // convert "water threshold" to "waterThreshold"
-  systemStatus.waterThreshold = systemStatus["water threshold"];
-  delete systemStatus["water threshold"];
-
-  // convert "time left" to "timeLeft"
-  systemStatus.pump.timeLeft = systemStatus.pump["time left"];
-  delete systemStatus.pump["time left"];
-
-  // add field "updated"
-  systemStatus.updated = Date.now();
-  return systemStatus;
-}
-
 // Async thunks
 export const startPump = createAsyncThunk(
   'systemStatus/startPump',
   async ({ api, pouringTime }, { dispatch }) => {
-    console.log('startPump: pouringTime = ' + pouringTime);
     const response = await api.start(pouringTime);
     return response;
   }
@@ -28,7 +12,6 @@ export const startPump = createAsyncThunk(
 export const stopPump = createAsyncThunk(
   'systemStatus/stopPump',
   async ({ api }, { dispatch }) => {
-    console.log('stopPump');
     const response = await api.stop();
     return response;
   }