Can I use one cleansing product twice?

On days when I wear light makeup, I sometimes skip double cleansing and finish with just the first step, but on days when I wear heavy makeup, I double cleanse.

When I double cleanse, I usually use two products.

After washing my face for the first time with cleansing water, I wash it for the second time with a foam cleanser.

But is it okay to double cleanse using only one product?

Are there any downsides to double cleansing with only one product?

Do I really have to use two things?