Water is a great solvent. It’s neutral and doesn’t provide any strong positive or negative effects. It just helps components to mix better and to transport active components.
Vitamin C is known for its strong antioxidant activity. It helps to slow down aging processes. The other positive effect of this ingredient is that it helps to make skin tone even. It's a great ingredient to counter dark areas and uneven skin tone. It's well-researched and considered safe. But it's acid and can irritate the skin if used too often.
PEG-40 Hydrogenated Castor Oil helps ingredients to mix better. It has nice cleansing activity helping to remove sebum and dirt from the surface of your skin. It's also responsible for making soft foam in soaps, shower gels, etc. Despite it having "PEG" in the title, it's considered to be safe.