Whilst adding water will in some cases facilitate easier placing, the disadvantages of this include the following:
1.Lower compressive strengths.
2.Segregation of the concrete mix under certain conditions resulting in variable quality throughout the concrete mass.
3.Cracking - with too much water, there will be lower tensile strength, and a tendency towards high shrinkage and subsequent cracking.
4.Dusting and scaling - bleeding of excess water brings too many fines to the surface of floors.
5.Sand streaks - excess water bleeding up the sides of forms washes out cement paste and leaves an unsightly streaked surface.
6 Contamination - too much water in concrete placed on grades causes contamination from the subgrade with the concrete leading to an array of quality problems.
7.Permeability - voids left as excess water evaporates invite water to seep through walls and floors.
8.Dead losses - costly repairs, or in extreme cases, demolition and re-building at contractor's expense.