Water Heavy Bags
 

I found it very difficult to find any good information on water heavy bags on the internet, so after a lot of searching and finally getting one, I did a write up here
Water-Filled Heavy Punching Bags on my findings and thoughts.

I have a 70 pound bag that has a water core to it.

I can't remember the brand-name right now, but it is pretty nice.

How well does leather stand up to being drenched in sweat I wonder?

is it a century hydrocore? i know those come in 70lbs and are quite common. its not leather is it? i believe the salt in the sweat would cure the leather more and dry it. nothing bad.

i'm kinda curious about these water bags every club i knew that had one all say they started leaking within a year, but then again that is commercial use not home use where a bag can go un used for weeks at a time

I've used them. They tend to wobble and move a lot more than other heavy bags. Just get a heavy bag. 100lbs, or a thai bag. the value and worth goes way farther.
i made this video of my hitting my bag like a year ago, but this is my set up:
http://www.youtube.com/watch?v=UdstGQJSVpk

I used to have a 130lb water bag. It was one of the water/foam variety described in that article. And it was probably one of the most useless things I've ever owned.

I'm not sure what the actual model name was, it was a Combat Sports model.

Not only was it too short to train MMA (can't punch the head and kick the legs), but it also contained a metal ring at the top of the bag (I would assume the top of the badder), that made my knuckles ache for weeks after I stopped using it, through 16oz gloves after they'd been worn down with a little use. This same metal ring got dislodged and misaligned by the accumulation of a few weeks worth of uppercuts and just one front snap that was the "straw that broke the camels back." Another issue I found with the water/foam design is that you have to penetrate 2-3 inches into the bag with each technique before connecting with a rigid surface that resists the impact.

The point I'm trying to make is that I'm not the most vigorous guy when it comes to training, not by a long shot, and I broke this bag beyond repain in less than a month. Suffice to say, I'm permanently butthurt on waterbags.

As said above me, I'd recommend a heavy bag of Thai bag. More importantly I recommend from some company that makes things specifically for MMA and Boxing, and doesn't sell their product in Wal-Mart (don't go with everlast-one of those broke pretty easily too under my abuse!). Somewhere like Title for example. A friend has a Title Thai bag and it is so amazingly well build and stiff I get a little giddy every time I hit it.