How to calculate the final concentration of water in a solution when a solution was brought to the final volume with water?

I am not requesting the answer to the volume of stock solutions, simply wondering how once all of the volumes are attained and the volume of water is found, how I can then find the concentration of water. Looking for steps to finding concentration of water.

Given stock solutions, find volume of each reagent to give the indicated concentration when brought up to final volume with water.

Stock solution Final Concentration Volume 1 M Imidazole 50 mm 0.5 M MgCl2 10 mm 0.4 M NaCl 100 mm 0.2 M EDTA 2.5 mm Water Final Volume: 50mL