Index: Ringtoets/HydraRing/src/Ringtoets.HydraRing.Data/HydraulicBoundaryLocation.cs
===================================================================
diff -u -r57634f535a347ce49c2491f114d7238d5387c7a8 -r883060cccacd8501ff89325a242fc352c54e8a53
--- Ringtoets/HydraRing/src/Ringtoets.HydraRing.Data/HydraulicBoundaryLocation.cs	(.../HydraulicBoundaryLocation.cs)	(revision 57634f535a347ce49c2491f114d7238d5387c7a8)
+++ Ringtoets/HydraRing/src/Ringtoets.HydraRing.Data/HydraulicBoundaryLocation.cs	(.../HydraulicBoundaryLocation.cs)	(revision 883060cccacd8501ff89325a242fc352c54e8a53)
@@ -48,7 +48,7 @@
             Id = id;
             Name = name;
             Location = new Point2D(coordinateX, coordinateY);
-            DesignWaterLevel = Double.NaN;
+            DesignWaterLevel = double.NaN;
         }
 
         /// <summary>
Index: Ringtoets/Integration/src/Ringtoets.Integration.Service/DesignWaterLevelCalculationActivity.cs
===================================================================
diff -u -r6ccc539ce58e63f0e0fbff0da189c87b65146129 -r883060cccacd8501ff89325a242fc352c54e8a53
--- Ringtoets/Integration/src/Ringtoets.Integration.Service/DesignWaterLevelCalculationActivity.cs	(.../DesignWaterLevelCalculationActivity.cs)	(revision 6ccc539ce58e63f0e0fbff0da189c87b65146129)
+++ Ringtoets/Integration/src/Ringtoets.Integration.Service/DesignWaterLevelCalculationActivity.cs	(.../DesignWaterLevelCalculationActivity.cs)	(revision 883060cccacd8501ff89325a242fc352c54e8a53)
@@ -57,17 +57,23 @@
 
         protected override void OnRun()
         {
-            PerformRun(() => DesignWaterLevelCalculationService.Validate(assessmentSection.HydraulicBoundaryDatabase, hydraulicBoundaryLocation),
-                       () => hydraulicBoundaryLocation.DesignWaterLevel = double.NaN,
-                       () => DesignWaterLevelCalculationService.Calculate(assessmentSection,
-                                                                          assessmentSection.HydraulicBoundaryDatabase,
-                                                                          hydraulicBoundaryLocation,
-                                                                          assessmentSection.Name)); // TODO: Provide name of reference line instead
+            if (double.IsNaN(hydraulicBoundaryLocation.DesignWaterLevel))
+            {
+                PerformRun(() => DesignWaterLevelCalculationService.Validate(assessmentSection.HydraulicBoundaryDatabase, hydraulicBoundaryLocation),
+                           () => hydraulicBoundaryLocation.DesignWaterLevel = double.NaN,
+                           () => DesignWaterLevelCalculationService.Calculate(assessmentSection,
+                                                                              assessmentSection.HydraulicBoundaryDatabase,
+                                                                              hydraulicBoundaryLocation,
+                                                                              assessmentSection.Name)); // TODO: Provide name of reference line instead
+            }
         }
 
         protected override void OnFinish()
         {
-            PerformFinish(() => hydraulicBoundaryLocation.DesignWaterLevel = Output.Result, hydraulicBoundaryLocation);
+            if (double.IsNaN(hydraulicBoundaryLocation.DesignWaterLevel))
+            {
+                PerformFinish(() => hydraulicBoundaryLocation.DesignWaterLevel = Output.Result, hydraulicBoundaryLocation);
+            }
         }
     }
 }
Index: Ringtoets/Integration/test/Ringtoets.Integration.Service.Test/DesignWaterLevelCalculationActivityTest.cs
===================================================================
diff -u -r0f7eb2998561112d0013b667ee39c2316341d2fe -r883060cccacd8501ff89325a242fc352c54e8a53
--- Ringtoets/Integration/test/Ringtoets.Integration.Service.Test/DesignWaterLevelCalculationActivityTest.cs	(.../DesignWaterLevelCalculationActivityTest.cs)	(revision 0f7eb2998561112d0013b667ee39c2316341d2fe)
+++ Ringtoets/Integration/test/Ringtoets.Integration.Service.Test/DesignWaterLevelCalculationActivityTest.cs	(.../DesignWaterLevelCalculationActivityTest.cs)	(revision 883060cccacd8501ff89325a242fc352c54e8a53)
@@ -149,6 +149,32 @@
         }
 
         [Test]
+        public void Run_CalculationAlreadyRan_ValidationAndCalculationNotPerformed()
+        {
+            // Setup
+            var assessmentSection = new AssessmentSection(AssessmentSectionComposition.Dike);
+            ImportHydraulicBoundaryDatabase(assessmentSection);
+
+            var designWaterLevel = 3.0;
+            var hydraulicBoundaryLocation = new HydraulicBoundaryLocation(1, "test", 1, 1)
+            {
+                DesignWaterLevel = designWaterLevel
+            };
+
+            var activity = new DesignWaterLevelCalculationActivity(assessmentSection, hydraulicBoundaryLocation);
+
+            // Call
+            Action call = () => activity.Run();
+
+            // Assert
+            TestHelper.AssertLogMessages(call, messages =>
+            {
+                var msgs = messages.ToArray();
+                Assert.AreEqual(0, msgs.Length);
+            });
+        }
+
+        [Test]
         public void Finish_ValidCalculationAndRun_SetsDesignWaterLevelAndNotifyObservers()
         {
             // Setup
@@ -201,6 +227,30 @@
             mocks.VerifyAll();
         }
 
+        [Test]
+        public void Finish_CalculationAlreadyRan_FinishNotPerformed()
+        {
+            // Setup
+            var assessmentSection = new AssessmentSection(AssessmentSectionComposition.Dike);
+            ImportHydraulicBoundaryDatabase(assessmentSection);
+
+            var designWaterLevel = 3.0;
+            var hydraulicBoundaryLocation = new HydraulicBoundaryLocation(1, "test", 1, 1)
+            {
+                DesignWaterLevel = designWaterLevel
+            };
+
+            var activity = new DesignWaterLevelCalculationActivity(assessmentSection, hydraulicBoundaryLocation);
+
+            activity.Run();
+
+            // Call
+            activity.Finish();
+
+            // Assert
+            Assert.AreEqual(designWaterLevel, hydraulicBoundaryLocation.DesignWaterLevel);
+        }
+
         private void ImportHydraulicBoundaryDatabase(AssessmentSection assessmentSection)
         {
             string validFilePath = Path.Combine(testDataPath, "HRD dutch coast south.sqlite");