5 1/4 cups water, divided
1 1/4 cups white sugar
1 cup sliced fresh rhubarb
1 pinch salt
1 cup fresh lemon juice
Fresh rhubarb stalks, for garnish
Stir 1 1/4 cups water, sugar, rhubarb, and salt in a small saucepan. Bring to a boil, stirring to dissolve sugar. Reduce heat to medium-low and simmer to the consistency of syrup, about 6 minutes. Strain through a fine-mesh sieve set over a Mason jar; discard solids. Chill, covered, at least 1 hour.
Stir chilled rhubarb syrup, remaining 4 cups water, and lemon juice in a large pitcher. Chill until ready to serve. Pour into ice-filled glasses. Garnish with fresh rhubarb stalks.