In a saucepan, combine the chopped rhubarb and water. Bring to a boil over medium heat.

Reduce heat and simmer for about 15 minutes, until the rhubarb is soft.

Remove from heat and strain the mixture through a fine mesh strainer into a bowl, discarding the solids.

Return the liquid to the saucepan, add sugar and lemon juice, and heat over medium heat until the sugar dissolves.

Allow the syrup to cool, then transfer it to a bottle or jar for storage.