The injection of the water would result in the dilution of the plasma. The dilution of the blood plasma would make it hypotonic as compared to the red blood cells present in the plasma.
In the hypotonic plasma, the red blood blood cell would cell. The red blood cell would allow the water molecules to come inside and as a result of inflow of the water, the cell will swell and probably burst. So, the red blood cells at the site of injection will swell and burst due to the injection of water.