The difference, by the numbers
They have no ingredient in common: the Ranch Water has tequila, triple sec, lime juice and soda water, the Sex on the Beach vodka, peach schnapps, orange juice and cranberry juice. In parts, a Ranch Water is 2 tequila, 1 triple sec, 1 lime and 4 soda; a Sex on the Beach is 2 vodka, 1 peach schnapps, 2 orange and 2 cranberry. By volume, the Ranch Water is 50% mixer and juice, 25% spirit, 13% liqueur and 12% citrus; the Sex on the Beach is 57% mixer and juice, 29% spirit and 14% liqueur. Different bottles, similar balance: that makes them close cousins on the ratio map.
The Ranch Water is the stronger drink in the glass (13.3% ABV against 12.7%) and holds more alcohol (2.03 standard drinks against 1.10). The Ranch Water has more calories (about 237 against 170), but the Sex on the Beach has more sugar (13.6 g against 8.0 g). Both are built and served in a highball.