Hola Houston! Need the best sandia for my fiancee’s agua fresca!

My fiancee is an amazing cook, thanks to her ta and their heirloom cookbook full of Matamoros family recipes. I can't compete in the kitchen, but I want to surprise her with the juiciest, sweetest watermelon for the delicious agua fresca she makes for the whole family.

Where do y'all find the best sandia in Houston? Farmers markets, tiendas, anywhere with top-notch watermelon? There's a lot of pressure to get this right, so any tips are appreciated. Gracias!