In the past, if you found your ball inside the red or yellow lines/stakes of a water hazard — but not in the water itself and with a chance to play it — you had to proceed with extreme caution.
You could not remove loose impediments, ground your club, or take a practice swing that touched anything in that hazard. Additionally, a whole host of other ‘touch’ rules applied to the situation, too.
With the 2019 Rules changes, water hazards are now called “penalty areas” — and many of those past touch restrictions have been removed.
Starting in 2019, if you find your ball within a yellow- or red-lined penalty area with the chance to play it, your pre-shot routine can be the same as if you had found the ball anywhere else on the golf course:
You may remove loose impediments.
You may take a couple of practice swings that touch the ground.
You may ground your club behind the ball before you swing.
(But still as before, none of these actions may be done to improve conditions for the stroke.)
Treating pre-shot actions the same way for both the general area and the penalty area eliminates rules confusion and reduces pointless penalties. That’s a smart revision.