Section grapefruit, removing membrane and leaving slices whole or in large pieces. Place the grapefruit sections in a stainless steel or plastic mesh colander, and allow to drain for at least 15 minutes. 

In a small saucepan, combine water and strawberries. Bring to a boil, crushing strawberries. Simmer for 3-4 minutes.

Strain the strawberries with a mesh strainer, reserving the liquid and pressing the pulp through the strainer. Discard the remaining pulp.

In same saucepan, return strawberry juice, whisking in the cornstarch and the sugar. Stir continuously over medium low heat, until the mixture forms a clear and thick gel. Remove from the heat and set aside. 

Divide the grapefruit sections and strawberry gel into 1/3 portions. Spread a 1/3 of the gel in the pie shell. Arrange 1/3 of the grapefruit sections in the prepared pie crust. Spread another 1/3 of the gel on top of the grapefruit sections, and add another 1/3 portion of grapefruit sections. Cover the grapefruit with the final layer of strawberry gel, cover with plastic and store in the refrigerator. Reserve the final 1/3 portion of grapefruit sections for garnish. 

Chill for about three hours before serving. Garnish with the last 1/3 portion of grapefruit sections. Serve with whipped cream and top with fresh mint leaves.