1. Combine 450g (1 pound) of rhubarb and 300g (1 1/3 cups) granulated sugar in a large pot. Let it sit for 30 minutes to allow the rhubarb to release its juices and the sugar to dissolve.

2. Add 775ml (3 1/4 cups or 26.3 US fluid ounces) of water to the pot and bring to a boil over high heat (around 100°C or 212°F). Reduce the heat to medium-low (around 150°C is incorrect, use 180°C or 356°F is better for simmering but a more realistic value is around 90-95°C or 195°F for a gentle simmer) and simmer for 10 minutes, or until the rhubarb is tender and the liquid has reduced slightly.

3. Remove the pot from the heat and let it cool slightly. Strain the mixture through a cheesecloth or fine-mesh sieve into a large bowl, pressing on the solids to extract as much liquid as possible. Discard the rhubarb.

4. Stir in 120ml (1/2 cup or 4 US fluid ounces) of freshly squeezed lemon juice and let the syrup cool to room temperature (around 20°C or 68°F). Refrigerate or freeze for later use.

5. To serve, mix 1 part syrup with 2 parts water (or to taste) and enjoy as a refreshing beverage. You can also use this syrup as a topping for ice cream, pancakes, or waffles.