Water storage
All our water comes from rain
Most precipitation evaporates, is taken up by plants, or flows to the sea. Some of it ends up as groundwater.
Why is storage limited? The Gulf Islands lack high mountains with winter snow that store water into the summer months. As well, there are few lakes and most are small and the water that can be stored in fractured rock under the islands is limited.
With your wet winters, you must have lots of water.
Sadly, that's not true. Most winter rains evaporate, are taken up by plants, or flow in streams to the sea. Only a small amount is stored.