To make it difficult for the ice cubes to melt, here are a few things you can try:
Boiling water before cooling: Boiling the water and then pouring it into an ice tray during the cooling process allows oxygen and other impurities to be released from the water, resulting in purer ice cubes.
Plant-based additives: Plant-based ingredients, such as mint or lemon peel, can be added to the water to stabilize the ice cubes and make them more difficult to melt.
Use a vacuum-sealed fresh-keeping bag: You can pour water into a vacuum-sealed fresh-keeping bag and put it in the refrigerator, which will slow down the evaporation of water and make it less likely for the ice cubes to melt.
Freeze in a low freezer: When making ice cubes, you can freeze the ice tray by placing it in a freezer at a low temperature. This allows the ice cubes to freeze more thoroughly, making them firmer and more difficult to melt.
Use light-coloured containers: Store the ice in buckets, and try to choose the lightest-coloured buckets or containers. Light colors absorb much less heat, which in turn slows down the rate at which the ice melts.
It is important to note that the above methods can make it harder for ice cubes to melt, but they do not completely prevent it from melting. In high temperatures, the ice will still melt. So, in order to keep cold drinks cool during the hot summer months, it is best to keep them in the refrigerator or freezer to ensure optimal condition.