Even the smallest splash of water on your fresh spray tan can result in light spots or a streaky appearance, something that you will really want to avoid. Coming back into the salon to touch up the area with spray tan would be recommended, or carefully use a self-tan to even it out.
You can also disguise this by choosing a bronzer that closely matches your tanned skin colour. Rub it evenly into the affected areas until it blends in. You will have to do this daily or whenever you go out until the tan fades away.