It is important to remember that VIC is about long-term trends and not about daily activity. The VIC is affected by the VWC of the soil, and if you use vertical rulers to measure it, you will see that there are differences in VWC, which affects the VIC. When water is added, two things happen.

In the first place, water washes some ions off the clay particles, so depending on the previous VIC and the CEC of the soil you may see a short-term increase in VIC as ions disassociate and go into solution. It is possible to reduce VIC by simply adding water if there isn't a substantial ion concentration held by clay particles.

Here is an example to explain this more clearly. By adding a teaspoon of salt to a half-full glass of water, a known value of VIC can be obtained. If the water content is doubled by filling the glasswithout adding more salt, the concentration of ions has decreased by 50% because twice the amount of water has been added.