Cut watermelon into small pieces, small enough to put in a blender. Blend well, until there are no more chunks in the mixture. Strain thoroughly through a fine mesh sieve (preferably, add a layer of kitchen paper towel to make sure there is no pulp in the strained juice).
Juice lime and lemon well, straining to also make sure there is no pulp.
Mix all the juices together in a large vessel, then add simple syrup and orange blossom. Stir and you’re ready.
3.25 L Watermelon Juice
1 L Lime Juice
0.4 L Lemon Juice
0.4 L Simple Syrup
0.10 L Orange Blossom Water