Clean the rhubarb stalks and trim the root end. Chop the rhubarb stalks into 1-2 cm thick slices. Add to a stainless steel or enameled cast iron pot (non-reactive cookware) and toss with sugar. Rest 30 minutes.
Add the water and lemon juice and place on medium heat. Bring to a boil then lower the heat and simmer for 15 minutes, until the rhubarb is soft and the water becomes light pink.
Strain the syrup through a fine mesh sieve and into a clean glass bottle or jar. Keep refrigerated.
Notes
The nutritional information provided is only meant as a guideline and takes into account only a small serving of syrup if enjoyed with water. If adding the rhubarb syrup to a different drink (like a cocktail) the final calorie count will be higher.