Question

1. We can use less water when we do the dishes.

2. We can use less water when we are doing the dishes.

3. We can use only a little water when we wash a car.

4. We can use only a little water when we are washing a car.
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Are they all grammatical? What is the difference between the ing form and the base form?

Answer 1

All are fine.

The present and the present progressive tenses are both used correctly. The progressive seems to give the feeling of current action to each of those sentences.