Anyway, I would start with the easy stuff and compare the bills/electrical usage for all the units first.

The point is, killing is rarely a proportionate response to the provocation, so blaming the provocateur seems inappropriate.

Are your solar panels net producers above your usage, so that your electric utility pays you?

Since I don't know your market and tenant base, I would be inappropriate for me to make any suggestion.

One thing I look for is cash flow/cap rate after the best usage of the property, whether that means adding a unit, ect. 

Of course, it is important that you take pre-move in photos and inspection sheets with the tenants signatures to substantiate any claim of intentional damages that may have occurred.As for the disposal, well they go depending on usage and what exactly people are putting in them...

At first I thought it may be a good way to add value by managing water usage and expenses but it sounds like it's more trouble than it's probably worth...  

Planning to rent out one of the unit, what should I do is a better option towards amount charge to the tenant about gas and electricity usage?

But that is some low hanging fruit that I’ll need to address to get highest and best usage out of them.

The current owners had been using as mixed use residential/ commercial.Does anyone have experience good or bad with grandfathered usage.