Fresh water, a legal sewage system and availability of electricity, telephone and internet all belong to civilised island life.
One could perhaps spare electricity, telephone and internet, but not water! If there is no water on the island and the ground water table has sunk so deep that it cannot serve the plants, the island dries out and becomes unappealing. The only way to get water is to use a desalination system (costs up to US $50,000). A drilled well is ideal. Almost all islands in the northern hemisphere and in the very southern hemisphere have this. When considering the purchase of an island around the equator, the availability of water needs to be on your checklist. An island with its own water supply automatically has a greater value.
Electricity can be generated today by using alternative methods. Still, the ideal situation would be to run underwater cables from the mainland to the island. The initial costs are high, but as time progresses, this is a more comfortable option. A telephone line can also be installed, however with today’s cellular network, this is no longer a big issue.