What is the real and / or the best "agua de valencia" recipe?!

On the net I found different recipes, according to some there should be 50% orange juice and 50% cava, according to others 25% orange juice and 75% cava. And some had cointreau, some had sugar, ...

Could anyone tell me a good recipe?! Would like to serve agua de valencia for my friends on my birthday.

Many thanks, Katja