- In a 3-quart saucepan, combine the water, rhubarb, sugar, zest, and salt; bring to a boil, stirring occasionally, until the sugar is dissolved.
- Decrease heat to a simmer; cover, and cook until the rhubarb is soft, about 10 minutes.
- Add in the quartered strawberries; cook for 4 minutes.
- Remove from heat and let cool for 15 minutes.
- Strain fruit mixture through a fine-mesh strainer into a 2-quart container, pushing down on the solids to extract as much juice as possible.
- Add vanilla and lemon juice; stir to combine.
- Let cool completely, then chill until very cold.
- When ready to serve, add the sliced strawberries and serve over ice.