Hello Julienne,
It certainly sounds like you've already been doing some super smart research and planning towards your upcoming visit to the magic of Walt Disney World Resort!
As you rightly mention, there are numerous online Disney fan-sites which can help Guests predict which days of the week are potentially best for visiting the Disney Parks, I know this is something I've done in past yEars to gain the most from my precious family time. As for the best days of the weeks to spend time at either of Disney's splashtastic water parks;
Disney's Typhoon Lagoon Water Park and
Disney's Blizzard Beach Water Park in my own experience I would say the weekends are usually busier with local families enjoying the parks and of course during any public holiday or peak summer season.
Other than that I think most anytime is a great time for a Disney water park day, although I would suggest an early arrival time on a hot day so you can easily find a shady spot to lounge in.
One of my best family memories of time spent at Disney's Typhoon Lagoon Water Park is when we rented a
Beachcomber Shack; these wonderfully private spaces accommodate up to 6 Guests in total shaded comfort with amenities such as loungers, towels, refillable drinks plus a cooler filled with bottled water and the friendly services of a Beach Attendant.
Be sure to check Disney water Park opening times and schedules via
Park Hours & Calendars and also take a peek at this
Disney Parks Blog ~ Moms Panel Monday ~ Water Parks Fun at Walt Disney World Resort.
~ Jane