squealing alt belt?

renault megane 1.6 petrol
just replaced alt belt but it still squeales for about 10 mins before it goes quiet when engine warm, been doing this a while now.

2 weeks ago i had to top up coolant by 1 ltr of water and the other day when replacing belt i had top up coolant again. im thinking water pump could be slowly leaking water. engine runs fine and doesnt overheat. any other ideas. thanks