In a large bowl, whisk the heavy cream for a few minutes until you've got stiff peaks.
Carefully fold in the condensed milk then pour the mixture into a large container suitable for freezing.
Add the strawberries, sugar and water into a blender. Process for 1 minute - scraping down the sides of the blender as necessary - until the strawberries have totally broken down.
Pour the strawberry mixture in an even layer on top of the ice cream in the container. Use a spoon or knife to draw swirled patterns through the strawberry layer into the ice cream, so the two layers get swirled together.