Index: firmware/App/Controllers/DGInterface.c
===================================================================
diff -u -r981de1f5228152ec6877aceae3d66ebf5efc7101 -r633861a3e472c1a288fa10a52ec0f7e7153e4dce
--- firmware/App/Controllers/DGInterface.c	(.../DGInterface.c)	(revision 981de1f5228152ec6877aceae3d66ebf5efc7101)
+++ firmware/App/Controllers/DGInterface.c	(.../DGInterface.c)	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -60,7 +60,6 @@
 static U32 dgSubMode = 0;                                       ///< Current state (sub-mode) of current DG operation mode.
 static BOOL dgStarted = FALSE;                                  ///< Flag indicates whether we have commanded the DG to start or stop.
 static BOOL dgTrimmerHeaterOn = FALSE;                          ///< Flag indicates whether we have commanded the DG to start or stop the trimmer heater.
-static BOOL dgWaterSampled = FALSE;                             ///< Flag indicates whether we have commanded the DG to sample water.
 
 // State machine states
 /// Current state of treatment mode reservoir management.
@@ -127,7 +126,6 @@
 
     dgStarted = FALSE;
     dgTrimmerHeaterOn = FALSE;
-    dgWaterSampled = FALSE;
     dgPrimaryTempSet = 0.0;
     dgTrimmerTempSet = 0.0;
     dgActiveReservoirSet = DG_RESERVOIR_2;
@@ -856,10 +854,9 @@
  * @details Outputs: sample water command sent to DG.
  * @return none
  *************************************************************************/
-void cmdDGSampleWater( void )
+void cmdDGSampleWater( SAMPLE_WATER_CMD_T cmd )
 {
-    dgWaterSampled = TRUE;
-    sendDGSampleWaterCommand();
+    sendDGSampleWaterCommand( cmd );
 }
 
 /*********************************************************************//**
Index: firmware/App/Controllers/DGInterface.h
===================================================================
diff -u -r981de1f5228152ec6877aceae3d66ebf5efc7101 -r633861a3e472c1a288fa10a52ec0f7e7153e4dce
--- firmware/App/Controllers/DGInterface.h	(.../DGInterface.h)	(revision 981de1f5228152ec6877aceae3d66ebf5efc7101)
+++ firmware/App/Controllers/DGInterface.h	(.../DGInterface.h)	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -151,8 +151,8 @@
 void cmdStartDGFill( U32 fillToVolMl );
 void cmdStartDGDrain( U32 drainToVolMl, BOOL tareLoadCell );
 void cmdStartDGTrimmerHeater( void );
-void cmdStopDGTrimmerHeater( void );
-void cmdDGSampleWater( void );
+void cmdStopDGTrimmerHeater( void );
+void cmdDGSampleWater( SAMPLE_WATER_CMD_T cmd );
 
 void handleDGCommandResponse( DG_CMD_RESPONSE_T *dgCmdRespPtr );
 BOOL getDGCommandResponse( U32 commandID, DG_CMD_RESPONSE_T *cmdRespPtr );
Index: firmware/App/Modes/ModePreTreat.c
===================================================================
diff -u -r981de1f5228152ec6877aceae3d66ebf5efc7101 -r633861a3e472c1a288fa10a52ec0f7e7153e4dce
--- firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision 981de1f5228152ec6877aceae3d66ebf5efc7101)
+++ firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -22,6 +22,7 @@
 #include "PreTreatmentRecirc.h"
 #include "Prime.h"
 #include "SelfTests.h"
+#include "SampleWater.h"
 #include "SystemCommMessages.h"
 
 /**
@@ -43,6 +44,7 @@
 
 static void resetSignalFlags( void );
 
+static HD_PRE_TREATMENT_MODE_STATE_T handleWaterSampleState( void );
 static HD_PRE_TREATMENT_MODE_STATE_T handleSelfTestNoCartState( void );
 static HD_PRE_TREATMENT_MODE_STATE_T handleInstallState( void );
 static HD_PRE_TREATMENT_MODE_STATE_T handleSelfTestDryState( void );
@@ -61,6 +63,7 @@
 {
     currentPreTreatmentState = HD_PRE_TREATMENT_START_STATE;
 
+    initSampleWater();
     initPrime();
     initSelfTests();
 
@@ -98,14 +101,12 @@
     switch ( currentPreTreatmentState )
     {
         case HD_PRE_TREATMENT_START_STATE:
-            cmdStartDG();
-            cmdSetDGDialysateTargetTemps( 39.0, 37.0 );
+            transitionToSampleWater();
             currentPreTreatmentState = HD_PRE_TREATMENT_WATER_SAMPLE_STATE;
             break;
 
         case HD_PRE_TREATMENT_WATER_SAMPLE_STATE:
-            transitionToNoCartSelfTests();
-            currentPreTreatmentState = HD_PRE_TREATMENT_SELF_TEST_NO_CART_STATE;
+            currentPreTreatmentState = handleWaterSampleState();
             break;
 
         case HD_PRE_TREATMENT_SELF_TEST_NO_CART_STATE:
@@ -219,6 +220,28 @@
 
 /*********************************************************************//**
  * @brief
+ * The handleWaterSampleState function handles patient connection state
+ * during pre-treatment mode.
+ * @details Inputs: none
+ * @details Outputs: requested mode transition to treatment mode
+ * @return current state (sub-mode)
+ *************************************************************************/
+static HD_PRE_TREATMENT_MODE_STATE_T handleWaterSampleState( void )
+{
+    HD_PRE_TREATMENT_MODE_STATE_T state = HD_PRE_TREATMENT_WATER_SAMPLE_STATE;
+
+    execSampleWater();
+
+    if ( TRUE == isSampleWaterPassed() )
+    {
+        state = HD_PRE_TREATMENT_SELF_TEST_NO_CART_STATE;
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
  * The handleSelfTestNoCartState function handles self-test with no cartridge.
  * @details Inputs: none
  * @details Outputs: home blood pump and dialysate pumps
Index: firmware/App/Modes/Prime.c
===================================================================
diff -u -r72551346728009770b22d327a1ac4fad8b5a1675 -r633861a3e472c1a288fa10a52ec0f7e7153e4dce
--- firmware/App/Modes/Prime.c	(.../Prime.c)	(revision 72551346728009770b22d327a1ac4fad8b5a1675)
+++ firmware/App/Modes/Prime.c	(.../Prime.c)	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -169,6 +169,8 @@
     switch ( currentPrimeState )
     {
         case HD_PRIME_START_STATE:
+            cmdStartDG();
+            cmdSetDGDialysateTargetTemps( 39.0, 37.0 );
             cmdSetDGActiveReservoir( DG_RESERVOIR_2 );
 #ifdef SKIP_PRIMING
             currentPrimeState = HD_PRIME_RESERVOIR_ONE_FILL_COMPLETE_STATE;
Index: firmware/App/Modes/SampleWater.c
===================================================================
diff -u
--- firmware/App/Modes/SampleWater.c	(revision 0)
+++ firmware/App/Modes/SampleWater.c	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -0,0 +1,200 @@
+/**************************************************************************
+*
+* Copyright (c) 2019-2021 Diality Inc. - All Rights Reserved.
+*
+* THIS CODE MAY NOT BE COPIED OR REPRODUCED IN ANY FORM, IN PART OR IN
+* WHOLE, WITHOUT THE EXPLICIT PERMISSION OF THE COPYRIGHT OWNER.
+*
+* @file SampleWater.c
+*
+* @author (last) Quang Nguyen
+* @date (last) 19-Feb-2021
+*
+* @author (original) Quang Nguyen
+* @date (original) 19-Feb-2021
+*
+***************************************************************************/
+
+#include "DGInterface.h"
+#include "HDDefs.h"
+#include "SampleWater.h"
+#include "TaskGeneral.h"
+
+/**
+ *  @addtogroup SampleWater
+ *  @{
+ */
+
+// ********** private definitions **********
+
+#define MAX_FLUSH_TIME_COUNT           ( 60 * MS_PER_SECOND / TASK_GENERAL_INTERVAL )   ///< Maximum flush time count relative to task general interval.
+
+// ********** private data **********
+
+static BOOL sampleWaterStartRequested;
+static BOOL sampleWaterStopRequested;
+static BOOL sampleWaterTakenConfirm;
+
+static SAMPLE_WATER_STATE_T currentSampleWaterState;
+static U32 flushTimerCounter;
+static BOOL sampleWaterPassed;
+static BOOL sampleWaterFailed;
+
+// ********** private function prototypes **********
+
+static SAMPLE_WATER_STATE_T handleWaterSampleSetupState( void );
+static SAMPLE_WATER_STATE_T handleWaterSampleState( void );
+static SAMPLE_WATER_STATE_T handleWaterSampleResultState( void );
+
+/*********************************************************************//**
+ * @brief
+ * The initSampleWater function initializes the Pre-Treatment SampleWater module.
+ * @details Inputs: none
+ * @details Outputs: SampleWater module initialized.
+ * @return none
+*************************************************************************/
+void initSampleWater( void )
+{
+    sampleWaterStartRequested = FALSE;
+    sampleWaterStopRequested = FALSE;
+    sampleWaterTakenConfirm = FALSE;
+
+    currentSampleWaterState = SAMPLE_WATER_SETUP_STATE;
+    flushTimerCounter = 0;
+    sampleWaterPassed = FALSE;
+    sampleWaterFailed = FALSE;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The transitionToSampleWater function prepares for transition to sample water mode.
+ * @details Inputs: none
+ * @details Outputs: Commanded DG to flush filters and re-initializes SampleWater module
+ * @return none
+*************************************************************************/
+void transitionToSampleWater( void )
+{
+    cmdDGSampleWater( SAMPLE_WATER_CMD_FLUSH );
+
+    initSampleWater();
+}
+
+/*********************************************************************//**
+ * @brief
+ * The execSampleWater function executes the Sample Water state machine.
+ * @details Inputs: currentSampleWaterState
+ * @details Outputs: currentSampleWaterState
+ * @return none
+*************************************************************************/
+void execSampleWater( void )
+{
+    switch ( currentSampleWaterState )
+    {
+        case SAMPLE_WATER_SETUP_STATE:
+            currentSampleWaterState = handleWaterSampleSetupState();
+            break;
+
+        case SAMPLE_WATER_STATE:
+            currentSampleWaterState = handleWaterSampleState();
+            break;
+
+        case SAMPLE_WATER_RESULT_STATE:
+            currentSampleWaterState = handleWaterSampleResultState();
+            break;
+
+        default:
+            // TODO: alarm
+            break;
+    }
+}
+
+/*********************************************************************//**
+ * @brief
+ * The isSampleWaterPassed function returns the result of sample water.
+ * @details Inputs: sampleWaterPassed
+ * @details Outputs: none
+ * @return TRUE if sample water result passed, otherwise FALSE
+ *************************************************************************/
+BOOL isSampleWaterPassed( void )
+{
+    return sampleWaterPassed;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handleWaterSampleSetupState function waits for filter flush period elapsed.
+ * @details Inputs: flushTimerCounter
+ * @details Outputs: none
+ * @return current state
+*************************************************************************/
+static SAMPLE_WATER_STATE_T handleWaterSampleSetupState( void )
+{
+    SAMPLE_WATER_STATE_T state = SAMPLE_WATER_SETUP_STATE;
+
+    if ( MAX_FLUSH_TIME_COUNT < flushTimerCounter++ )
+    {
+        state = SAMPLE_WATER_STATE;
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handleWaterSampleState function passes sample water commands from user
+ * down to DG.
+ * @details Inputs: sampleWaterTakenConfirm, sampleWaterStartRequested, sampleWaterStopRequested
+ * @details Outputs: Processed commands from user
+ * @return current state
+*************************************************************************/
+static SAMPLE_WATER_STATE_T handleWaterSampleState( void )
+{
+    SAMPLE_WATER_STATE_T state = SAMPLE_WATER_STATE;
+    DG_CMD_RESPONSE_T dgCmdResp;
+
+    if ( TRUE == sampleWaterTakenConfirm )
+    {
+        sampleWaterTakenConfirm = FALSE;
+        state = SAMPLE_WATER_RESULT_STATE;
+    }
+
+    if ( TRUE == sampleWaterStartRequested )
+    {
+        sampleWaterStartRequested = FALSE;
+        cmdDGSampleWater( SAMPLE_WATER_CMD_START );
+    }
+
+    if ( TRUE == sampleWaterStopRequested )
+    {
+        sampleWaterStopRequested = FALSE;
+        cmdDGSampleWater( SAMPLE_WATER_CMD_STOP );
+    }
+
+    if ( ( TRUE == getDGCommandResponse( DG_CMD_START_DRAIN, &dgCmdResp ) ) && ( DG_CMD_REQUEST_REJECT_REASON_FLUSH_EXPIRED == dgCmdResp.rejected ) )
+    {
+        cmdDGSampleWater( SAMPLE_WATER_CMD_FLUSH );
+        state = SAMPLE_WATER_SETUP_STATE;
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handleWaterSampleResultState function triggers a fault if user
+ * provides failed sample water result.
+ * @details Inputs: sampleWaterFailed
+ * @details Outputs: triggers a fault alarm
+ * @return current state
+*************************************************************************/
+static SAMPLE_WATER_STATE_T handleWaterSampleResultState( void )
+{
+    if ( TRUE == sampleWaterFailed )
+    {
+        // TODO: Trigger fault
+    }
+
+    return SAMPLE_WATER_RESULT_STATE;
+}
+
+/**@}*/
Index: firmware/App/Modes/SampleWater.h
===================================================================
diff -u
--- firmware/App/Modes/SampleWater.h	(revision 0)
+++ firmware/App/Modes/SampleWater.h	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -0,0 +1,43 @@
+/**************************************************************************
+*
+* Copyright (c) 2019-2021 Diality Inc. - All Rights Reserved.
+*
+* THIS CODE MAY NOT BE COPIED OR REPRODUCED IN ANY FORM, IN PART OR IN
+* WHOLE, WITHOUT THE EXPLICIT PERMISSION OF THE COPYRIGHT OWNER.
+*
+* @file SampleWater.h
+*
+* @author (last) Quang Nguyen
+* @date (last) 19-Feb-2021
+*
+* @author (original) Quang Nguyen
+* @date (original) 19-Feb-2021
+*
+***************************************************************************/
+
+#ifndef __SAMPLE_WATER_H__
+#define __SAMPLE_WATER_H__
+
+#include "HDCommon.h"
+
+/**
+ *  @defgroup SampleWater SampleWater
+ *  @brief SampleWater sub-mode of pre-treatment mode. This sub-mode allows user to sample water and enter manual test result.
+ *
+ *  @addtogroup SampleWater
+ *  @{
+ */
+
+// ********** public definitions **********
+
+// ********** public function prototypes **********
+
+void initSampleWater( void );
+void transitionToSampleWater( void );
+
+void execSampleWater( void );
+BOOL isSampleWaterPassed( void );
+
+/**@}*/
+
+#endif
Index: firmware/App/Services/SystemCommMessages.c
===================================================================
diff -u -r981de1f5228152ec6877aceae3d66ebf5efc7101 -r633861a3e472c1a288fa10a52ec0f7e7153e4dce
--- firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision 981de1f5228152ec6877aceae3d66ebf5efc7101)
+++ firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -681,18 +681,21 @@
  * The sendDGSampleWaterCommand function constructs a DG sample water command
  * message and queues the msg for transmit on the appropriate CAN channel.
  * @details Inputs: none
- * @details Outputs: DG sample water command msg constructed and queued.
+ * @details Outputs: DG sample water command msg constructed and queued.
+ * @param cmd sample water sub-command
  * @return TRUE if msg successfully queued for transmit, FALSE if not
  *************************************************************************/
-BOOL sendDGSampleWaterCommand( void )
+BOOL sendDGSampleWaterCommand( SAMPLE_WATER_CMD_T cmd )
 {
     BOOL result;
     MESSAGE_T msg;
 
     // Create a message record
     blankMessage( &msg );
     msg.hdr.msgID = MSG_ID_DG_SAMPLE_WATER_CMD;
-    msg.hdr.payloadLen = 0;
+    msg.hdr.payloadLen = sizeof( U32 );
+
+    memcpy( msg.payload, &cmd, sizeof( U32 ) );
 
     // Serialize the message (w/ sync, CRC, and appropriate CAN padding) and add serialized message data to appropriate comm buffer
     result = serializeMessage( msg, COMM_BUFFER_OUT_CAN_HD_2_DG, ACK_REQUIRED );
Index: firmware/App/Services/SystemCommMessages.h
===================================================================
diff -u -r981de1f5228152ec6877aceae3d66ebf5efc7101 -r633861a3e472c1a288fa10a52ec0f7e7153e4dce
--- firmware/App/Services/SystemCommMessages.h	(.../SystemCommMessages.h)	(revision 981de1f5228152ec6877aceae3d66ebf5efc7101)
+++ firmware/App/Services/SystemCommMessages.h	(.../SystemCommMessages.h)	(revision 633861a3e472c1a288fa10a52ec0f7e7153e4dce)
@@ -179,7 +179,7 @@
 BOOL sendDGStartStopTrimmerHeaterCommand( BOOL start, F32 trimmerHtrTemp );
 
 // MSG_ID_DG_SAMPLE_WATER_CMD
-BOOL sendDGSampleWaterCommand( void );
+BOOL sendDGSampleWaterCommand( SAMPLE_WATER_CMD_T cmd );
 
 // MSG_ID_DG_COMMAND_RESPONSE
 void handleDGCmdResp( MESSAGE_T *messagePtr );