In a large saucepan, combine the rhubarb, strawberries, water and sugar over low heat. Cover and cook, stirring occasionally, until the rhubarb and strawberries have broken down and the liquid is thick, 10-15 minutes.
Prepare Strawberry Rhubarb Ice Cream:
Heat the half and half on medium heat in a medium saucepan. While the cream is heating, whisk the egg yolks and 1/2 cup sugar together. Once the cream is simmering, slowly pour it into the egg yolks and sugar while whisking.
Pour back into the saucepan and turn the heat down to medium low. Stir in a figure 8 motion for several minutes until the mixture is thick enough to coat the back of a wooden spoon. Stir in 1 3/4 cups of the strawberry rhubarb puree.
Allow to chill completely in the refrigerator. Prepare in an ice cream machine according to manufacturer's instructions.
Prepare Strawberry Rhubarb Sorbet:
Add sugar and water to a medium saucepan. Bring the mixture to a boil and allow it to simmer until the sugar is completely dissolved, approximately 5 minutes.
Remove from the heat and allow it to cool briefly, then stir in 1 1/4 cups of the strawberry rhubarb puree. Allow to chill completely in the refrigerator. Prepare sorbet in an ice cream machine according to manufacturer's instructions.
Notes
To prepare only the ice cream or sorbet (as opposed to both), simply prepare half of the puree recipe.