Yes, I think. Thanks Lovestoscrap. But just to be sure. We are planning an 8 night/9 day stay at POP. Let's we buy an 8 day MYW ticket, with park hopper and water park. We couldn't go to the water park in the day, and then a theme park at night. Right? We would need a ten day MYW, with PH & WP. ????

Our original plan was to spend one or two days entirely at the water parks. But then we started thinking we could hit the water parks as a way to beat the midday heat, then go to the theme parks. But that does not look possible now. For $5 more, the ten day would be better for this plan. Right?
Wrong.
First of all, you will be in the area for a maximum of 9 days. Buying a 10-day theme park ticket would be wasteful, since you wouldn't be able to use more than 9 days' worth of theme park days.
Let me try to explain it differently than I did last time (obviously, I know that as I write this you haven't yet read my post above).
Let's say you buy the 8-day park hopper ticket with WPF&M option. All of these entitlements will be invisbly encoded onto one card that looks like a credit card of sorts.
But let's pretend that instead of that, you were given stacks of paper tickets.
One stack would be 8 theme park tickets (the 4 major parks). Another stack would be 8 WPF&M tickets.
Now ... hold on, this could get confusing ... because you are paying extra for the "park hopper" option on your theme park tickets, you are permitted to go to an unlimited number of theme parks in a day. So when you use one of those park hopper tickets, think of it as a sort of magical all-day all-access pass to the theme parks. You would use that same one (imaginary) paper ticket all day for one day. So let's say that it's Tuesday and you know you want to go to Animal Kingdom Tuesday morning and Magic Kingdom late Tuesday night. Remember the dumb example of having paper tickets ... you'll still be using that same one ticket for that day. That one paper theme park park hopper ticket will get you into BOTH of those parks on the same day.
So let's say that on that same Tuesday you ALSO wanted to hit both water parks. After Animal Kingdom you decide to go to Blizzard Beach. To get into Blizzard Beach, you have to give them one of your imaginary WPF&M paper tickets. Picture that they would take this ticket from you. Because it's a WPF&M ticket, it is good for only one admission, period ... that one ticket can't be used to get you into another WPF&M place later that day. Now let's say you're weird and have boundless energy and you want to go to Typhoon Lagoon immediately after Blizzard Beach on Tuesday. When you get to the gate at Typhoon Lagoon, you will have to give them ANOTHER (imaginary) paper WPF&M ticket.
So when you get back to your room on Tuesday night after you've done everything, you look at your stacks of tickets. Remember, you started with 8 theme park park hopper tickets, and 8 WPF&M tickets. You count your remaining tickets. You have 7 park hopper tickets left, and you have 6 WPF&M tickets left. Remember, going to both MK and AK on that day only cost you a total of ONE of your park hopper tickets. But going to 2 different water parks that day cost you a total of 2 of your WPF&M tickets.
I hope I've helped rather than confused ....