George 1,

The standard lagoon 450 has 1 tank with 92 gallons. There is a factory option for a second 92 gallon water tank. Out Lagoon 450 Scuba doo has that option. Therefore Scuba Doo has 184 gallons plus the hot water tank.

I could not imagine having only 100 gallons of water on board.

Warren S/V Scuba Doo
Lagoon 50 (winner of best crewed yacht under 55 feet at the St. Thomas crewed yacht boat show).

https://www.cyabrochure.com/ebn/2307/pdyrX/6642/4///