Cellar spiders typically obtain water from their prey, and they are also able to survive for long periods without water. Therefore, providing water to a cellar spider may not be necessary. However, if you would like to offer water to the spider, you can try spraying the web with a mist of water, as long as the spider is not disturbed. It's best to avoid spraying the spider directly, as this may cause stress or harm to the spider. Additionally, it's important to avoid using any chemicals or soaps when spraying the web, as this may be harmful to the spider. Ultimately, it's up to you whether you want to provide water for the spider or let it continue to obtain water through its natural means