Turtles are reptiles.
Reptiles include turtles, crocodilians, lizards, snakes and tuatara (found only in New Zealand).
Reptiles were the world's first truly terrestrial vertebrates. All reptiles have scaly skin that can withstand dessication and lay eggs with hard shells, therefore they are not tied to the water like their relatives, the amphibians. Since they can live on land, they also have an expanded lung system.
Amphibians consist of three groups of vertebrates: frogs, salamanders and caecilians (found in the tropics only). Amphibians have smooth, scaleless skin which is permeable to water. Water can evaporate easily from the skin, and an amphibian can dry up and die in a few hours if it does not have access to water. Thus amphibians tend to be active at times when evaporation is minimized: at night and when it rains.
However, this same skin permeability makes it possible for amphibians to obtain moisture from sources besides pools of water. This means that amphibians can live in very dry climates, like deserts, and when the dry season arrives, they just burrow underground and pull in moisture from the surrounding soil. Despite this, the amphibian's tie to water remains: their eggs must be laid in water in order to survive.