Obviously, water quantity cannot be decided based on the quantity mix design proportions only. There are other data which need to be known in order to be able to specify water content quantity for example, types of structural element, maximum aggregate size, and required workability. If these data are available, then the quantity of water can be easily computed from Table 6.3.3 of ACI 211.1-91.
Required slump can be determined based on the structural element type. Maximum aggregate size and slump value can be used to determine quantity of water for 1 meter cubic of concrete.