Q: Can Muslims use solar heated water?
A: The solar heating system used nowadays to hear water is permissible. The famous hadith which prohibits the use of water heated by the sun is frstly not so strong that it can be used to establish a binding rule of Islam, and secondly, the Ulema mention that the prohibition is health-related and does not fall under Islamic injunction. Some scholars have attached conditions to such water being harmful, such as exposure to direct sunlight at the equator or countries close to it, etc. (Raddul-Muhtaar).
And Allah Knows Best.