Two absolutely brilliant chapters. I am so glad to read that Harry actually has to work at his magic, much as in the nature of building up a muscle, rather than to suddenly learn and two days later master every aspect of magic in the known universe...and a couple others besides.
Your descriptions of that build-up, are well writ, and both informative and entertaining, especially when he learned how he'd screwed up with the water. He does seem to have an affinity with water, from his straw trick to modifying the temperature and humidity. Perhaps he's an elemental?
His letter to Minerva was not only funny, it also directly addressed a problem most of us have seen through the entire series. Seeing an angry Minerva going after Dumbledore, is gravy.
Their first meeting could have gone easier, but I suppose Harry showing her what he could do wandlessly after her wanded demonstration, would be rude.
His last response was great! "You have five hours to sell me your school."
As before, I eagerly await the next chapter of 'Elementary Calculations'. Alorkin
Biscuit to you. Yes, he is a water elemental. He will also be showing no one anything more than he has to. Even though he's known about his magic since he was eight Petunia still doesn't know that he knows.