What is the validity of an online website's claim regarding the effectiveness of reading specific Quranic verses in particular ways (such as: a certain number of times, blowing on water, drinking it, and anointing oneself with it) in treating various diseases like diabetes, high blood pressure, headaches, and other ailments?

Designating the recitation of specific verses a certain number of times for the treatment of particular diseases is not legislated except with specific evidence. What is not supported by evidence is closer to innovation (bid'ah). The entire Qur'an is a healing and a blessing, but claiming a specific effect for a particular verse requires evidence.