Help with getting my water to look good

Could someone tell what is they best height to put my map at? Cause the default height for my terrain is doesn’t let make my water the way it should so I set my location on landscape to -15000 and even at -19000 and I get beautiful water but it wont let me save my game afterwards or wont let me even test the map. But if I go back to default I can save my map and play it but with ugly water! Any ideas why this maybe?

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