Okay, I finally got the theme to work. By the way, when I ask for a link to the theme, I meant a link to the theme (Water 3). Not the website because the theme listed under his download section is Water 1.
There's two things that need to be changed for this to work: in your "style.php" file -- #title and #topmenu
Locate those in the file. They're close to the top and next to each other.
Under #title you need to change the line-height: to something like 35px.
Under #topmenu you need to change the margin-top: to something around 55px.
You mentioned you changed the text size and the margin in the #header but I'm assuming you meant the #title since the header doesn't have a text size.
The original #title had:
margin:38px 5px 0 0;
font-size:30px;
The numbers I gave you to add work with the original "style.php." You might have to adjust them because you changed some things. If you change the line-height in #title, then you need to change the margin-top in #topmenu, increasing or decreasing each one together. If you don't do this, then your top menu will drift away from your header image.