You should bring one gallon of water per person per day when you are hiking. It is important to stay hydrated, so if the weather is going to be hot, you may want to bring even more than that.
That all depends on how much hiking you are doing and how vigorous. But a normal hike (lasting about 1-2 hours), one bottle of water is good enough. Bring 2 bottles if you're hiking half day or more.
It depends on your age, how much you are going to exert yourself, terrain of area, temperature, etc. , but I would say that 3-5 litres would be suffice.
I would bring two big water bottles. You don't want to bring too much because you obviously have to carry it and you don't want to be lugging around huge bottles the whole time.
