Jim has addressed the first point: A wizard only has so much power to invest in their magical gizmos. At this point, Harry is rocking things like his staff, jacket, shield bracelet, and blasting rod (essential tools for amping up his wizardry) and so does not have the magical umph to spare.
Additionally, as OP as those potions were, they nearly got him killed, and are one-use only.
On the healing magic front: It is -incredibly- difficult. Listens To Wind has built his life around it, and even he cannot cure everything. Harry, who has less experience and less innate talent for slow, low watt magic, is unlikely to do anything meaningful with it.
Water Magic: Maybe you missed it, but Harry has been throwing around an awful lot of ice lately. Ice isn't, inherently, water magic, but Harry is still working within that realm.
I'm going to be a bit snarky here:
Healing magic: So Billy and the Werewolves
TM can learn to bend their shape-shifting abilities to heal wounds [ Side Jobs: Aftermath ], but Injun Joe has built his whole life around it... nah, shoe don't fit.
Potions: Removal of the potions is simply a literary device. No sane person would abandon a possible tactical advantage like that even if it was only the escape potion used in Storm Front by Harry and Susan and in Skin Game by Butters. But this way Harry actually gets his face kicked smashed and his ribs kicked in more often. Plain and simple.
Cold showers: Well... it's not like Harry _doesn't_have_ a water heater. It's just he "unhooked it". So Whenever Thomas or some lady-friend feel like a warm shower, the heater gets turned on. Pun intended. It's just not mentioned, because it's a long-running gag.
As far as Water magic goes, I'd say it has a lot to do with temperament. Ice and Fire [ The song of ] are fierce and cause harm. Water is... well, subtle, flows into small crevices, adapts it's shape, erodes things slowly. Somehow, that doesn't sound like Dresden to me. Even his Wind magic are insane gales and only after teaching Molly he stumbled upon a gentle application of wind magic... which he then uses to _clean_off_snow_. Sounds very gentle to me. Like a right hook is gentler because the other guy is wearing gloves.
Gizmos: The whole point in making those gizmos is so that they have magic stored up. The magic doesn't get permanently locked away, it get's regenerated when Harry eats, sleeps, rests properly. Remember Little Chicago? But if Harry actually would stick to the first rule about being a wizard; "To be prepared." we'd see him get kicked around a lot less. And while we pity him every time he gets beaten, stabbed, shot, burned, ... we still love the books because he gets beaten up and then gets up and keeps on fighting. Then, once fight isn't necessary he can fall over and get treated. For example: Take his silver bear charm from Blood rites paired with his Shield bracelet. Instead of channeling the magic through Harry simply create a connection between these two and the fights get a lot less exciting, because now Harry can create a barrier without straining himself too much while he casts some super-nuking spell. Yes, this is how a mage normally would operate [ well this or bringing a tank ], but it would soften the action scenes and make them less tense.
