Did you know that the Lake Tapps Reservoir holds about 14 billion gallons of water? And it takes 39 million gallons of water a day just to maintain the Lake Tapps Reservoir water level? That’s a lot of water! And it takes closer to 100 million gallons of water a day to slowly increase reservoir levels. To put that in perspective, the entire Seattle water service area uses 180 million gallons of water a day. Learn more here: Lake Tapps Lake Levels – Cascade Water.