I have to kill desert lizards for my slayer, but i have no idea how to get to them or survive in the desert. How do i get water skins? I need some advice

Go south of Al kharid. You see the pass, and some NPCs. Trade with shantay. You can buy both waterskins and a ticket to go trough the pass from him. Afterwards, you can take the flying carpet to Uzer (200 gp), or just walk south-east. Don't forget a knife to refill your water skins (use knife on kharidian cactus (healthy)). Alternatively, use fairy ring code DLQ.