When performing mandatory Ghusl, I often feel uncertain that water has reached every part of my body, especially my hair, leading to wasted time and water. How can I ensure the water reaches the roots of my hair effectively?
Repeated doubts in Ghusl or Wudhu or Prayers can be from Shaitan to disturb you. That is why Ahlul Bayt (AS) have ordered those who have repeated doubts to ignore such doubt and go ahead with out giving ant attention to the doubt.
Ignoring the repeated doubt will help you to get rid of it.
Wassalam.