Watermelon and lemon are two of the best fruits to alkalize the body.
if you read different forums, you will find those who take lemon drinks every day, and it is the basis of the master cleanse. Watermelon can be taken all by itself for part or all of a day or two or three. You can google watermelon cleanse on the CZ site. It cleanses the body, especially the kidneys while alkalizing.
Sweet fruits like dates and raisins are good for building, but due to high sugar you want to use them occasionally, not for 24 hours straight like watermelon.