An average size adult chicken will need to drink up to 500ml (1/2 litre) of water everyday depending on the temperature. Water should be constantly available whilst the chickens are active during the day.
Once they go in to roost your chickens don't need access to a drinker.
Your chickens drinker will need to be large enough that the hens can't knock it over. We'd suggest you use a drinker at least 1/2 gallon / 2 1/2 litres. Using a hanging drinker also helps prevent this.