Hi Kon,
Just seen your question about Symi water catchments. There have been on and off plans for a dam/reservoir for years but these have all failed so far for environmental and aesthetic reasons as it would be empty for most of the summer. Also geologically it would be a problem, as Symi is mainly limestone and extremely porous,so any dam would have to be lined with something to stop the water soaking away, and covered with something to prevent evaporation.
There is a spring at Vrisi, not far from my place, which is currently providing 400 tonnes a day to the local water supply thanks to the early rains.
Quite honestly, if we all continued to harvest the water from our roofs in the winter, not to mention the run off from the terraces, as they did in the old days, and regarded the water boat from Rhodes as a bonus instead of the main supply, we wouldn't do too badly. Even in a dry year we ourselves get more than 120 tonnes of water off our roof in the winter and never have enough cistern capacity to store it all!