Water dosing systems for concrete production are not as straight forward as first meets the eye. The dynamics of the materials change from batch to batch. Slight changes in the moisture content alter the water requirement and the results are variations in the workability (slump) of the mix. As new aggregates are delivered the moisture content will change and a new water content should be calculated to maintain the correct workability. This is impracticable in most cases and does not happen. This is particularly apparent in systems where a star type configuration is used to batch the aggregates. This form of batching almost ensures large variations in the moisture content of the aggregates. If your requirement is for the workability of the mix to remain consistent then water dosing is the answer. If however you need to maintain good material ratios, then moisture compensation is the correct route to follow.
Our company has gained valuable experience relating to this application over a number of years and has systems that can cater for these types of problems.