If you have booked a cottage at Lalandia, it always includes entrance tickets to Lalandia Aquadome.
You get electronic bracelets for the whole family, which can be used as both house key and entrance ticket. You can also load the bracelets with money so you can have a cashless stay in Lalandia.
Admission to the water park is valid for the entire stay, and if it is possible, even before check-in and after checkout.