Are these tongue and grove and will they leak water since I store items under it?

Hello, and thank you for reaching out regarding your question. While we do offer a grooved option for our board, it is designed to be used with our Hideaway hidden fastener system and not as a tongue and groove system. In addition to that we also want to advise you that the minimum gapping for width-to-width boards is a minimum of 3/16" of an inch which would allow water under the deck. We do make an additional product called RainEscapes which is a network of troughs and gutters to divert water from the deck. You can find more information about RainEscapes on our website Trex.com or call us at 1-800-289-8739 to speak with one of our Customer Care team members who would be happy to help you with any additional questions you may have.