diff --git a/pkg/sourcetransformer/examples/event_time_filter/impl/filter.go b/pkg/sourcetransformer/examples/event_time_filter/impl/filter.go
index 5e93c28b..3583c9ee 100644
--- a/pkg/sourcetransformer/examples/event_time_filter/impl/filter.go
+++ b/pkg/sourcetransformer/examples/event_time_filter/impl/filter.go
@@ -6,7 +6,7 @@ import (
 	"github.com/numaproj/numaflow-go/pkg/sourcetransformer"
 )
 
-func FilterEventTime(keys []string, d sourcetransformer.Datum) sourcetransformer.Messages {
+func FilterEventTime(_ []string, d sourcetransformer.Datum) sourcetransformer.Messages {
 	janFirst2022 := time.Date(2022, 1, 1, 0, 0, 0, 0, time.UTC)
 	janFirst2023 := time.Date(2023, 1, 1, 0, 0, 0, 0, time.UTC)
 	if d.EventTime().Before(janFirst2022) {
diff --git a/pkg/sourcetransformer/messaget.go b/pkg/sourcetransformer/messaget.go
index e7199a83..282b89ae 100644
--- a/pkg/sourcetransformer/messaget.go
+++ b/pkg/sourcetransformer/messaget.go
@@ -5,12 +5,7 @@ import (
 	"time"
 )
 
-var (
-	DROP = fmt.Sprintf("%U__DROP__", '\\') // U+005C__DROP__
-	// Watermark are at millisecond granularity, hence we use epoch(0) - 1 to indicate watermark is not available.
-	// eventTimeForDrop is used to indicate that the message is dropped hence, excluded from watermark calculation
-	eventTimeForDrop = time.Unix(0, -int64(time.Millisecond))
-)
+var DROP = fmt.Sprintf("%U__DROP__", '\\') // U+005C__DROP__
 
 // Message is used to wrap the data return by SourceTransformer functions.
 // Compared with Message of other UDFs, source transformer Message contains one more field,
@@ -60,9 +55,11 @@ func (m Message) Tags() []string {
 	return m.tags
 }
 
-// MessageToDrop creates a Message to be dropped
-func MessageToDrop() Message {
-	return Message{eventTime: eventTimeForDrop, value: []byte{}, tags: []string{DROP}}
+// MessageToDrop creates a Message to be dropped with eventTime.
+// eventTime is required because, even though a message is dropped, it is still considered as being processed,
+// hence the watermark should be updated accordingly using the provided event time.
+func MessageToDrop(eventTime time.Time) Message {
+	return Message{eventTime: eventTime, value: []byte{}, tags: []string{DROP}}
 }
 
 type Messages []Message
diff --git a/pkg/sourcetransformer/service_test.go b/pkg/sourcetransformer/service_test.go
index 5269deb0..d57d937e 100644
--- a/pkg/sourcetransformer/service_test.go
+++ b/pkg/sourcetransformer/service_test.go
@@ -79,7 +79,7 @@ func TestService_sourceTransformFn(t *testing.T) {
 		{
 			name: "sourceTransform_fn_forward_msg_drop_msg",
 			handler: SourceTransformFunc(func(ctx context.Context, keys []string, datum Datum) Messages {
-				return MessagesBuilder().Append(MessageToDrop())
+				return MessagesBuilder().Append(MessageToDrop(testTime))
 			}),
 			args: args{
 				ctx: context.Background(),
@@ -93,7 +93,7 @@ func TestService_sourceTransformFn(t *testing.T) {
 			want: &stpb.SourceTransformResponse{
 				Results: []*stpb.SourceTransformResponse_Result{
 					{
-						EventTime: timestamppb.New(eventTimeForDrop),
+						EventTime: timestamppb.New(testTime),
 						Tags:      []string{DROP},
 						Value:     []byte{},
 					},