We have self piercing water cooler bottle caps which fit all standard size water cooler bottles. 15/18.9/19 litre bottles.
Available in 50s or as a box of 500.
Simply fill your empty cooler bottle with cold fresh water and firmly push one of these caps on top. You can then place the newly filled bottle on top of your cooler and gently press down thus allowing the cap to self pierce and the water to enter the cooling chamber on your cooler.
Not only are you saving money on expensive pre-filled bottles but you are helping the planet too by eliminating the need for polluting vehicles to deliver your water.