Water: Fix reflection bug similar to Reflector.

examples/js/objects/Water.js

@@ -295,6 +295,9 @@ THREE.Water = function ( geometry, options ) {
 		renderer.shadowMap.autoUpdate = false; // Avoid re-computing shadows
 
 		renderer.setRenderTarget( renderTarget );
+
+		renderer.state.buffers.depth.setMask( true ); // make sure the depth buffer is writable so it can be properly cleared, see #18897
+
 		if ( renderer.autoClear === false ) renderer.clear();
 		renderer.render( scene, mirrorCamera );
 

examples/jsm/objects/Water.js

@@ -313,6 +313,9 @@ var Water = function ( geometry, options ) {
 		renderer.shadowMap.autoUpdate = false; // Avoid re-computing shadows
 
 		renderer.setRenderTarget( renderTarget );
+
+		renderer.state.buffers.depth.setMask( true ); // make sure the depth buffer is writable so it can be properly cleared, see #18897
+
 		if ( renderer.autoClear === false ) renderer.clear();
 		renderer.render( scene, mirrorCamera );