You might want to put a timer on the thermostat that turns it up and down depending on time of day or charge them over and above a certain amount of usage. 

For example, the tenant will pay a portion equal to the average of her last three months of water usage. 

Might be because of Californians being more drought-sensitive, but people are more careful about water usage these days.But, to be honest, I'd kill to have one, myself.

This is immoral and wrong on so many levels and was very inappropriately handled.Kind Regards,Jeff

But they have no hot water.Also, because I know this conversation is coming soon, am I obligated (again morally or legally) to pay any excessive gas charge, if they charge her for her full "usage"?

You can always get an idea of usage based off water bills. 

@Kenneth Garrett is right too overall rehabbing bathrooms and kitchens will raise your usage value higher than almost anything else apart from extra square footage or if you have limited space and too few bathrooms putting an extra bath in if you don't have enough room for an extra bedroom is a good choice as long as it doesn't contribute to any functional obsolescence ( that is as long as putting a bathroom in won't make the rest of the rooms too small for them to be usable)I would not agree with siding unless the exterior really needs a facelift and then I would just repair and paint unless you need to weather protect.

I absolutely agree which is why I had asked her on the 10th to keep reporting times/dates she smelled weed usage at the apartment so I could gather a timeline. 

As for water usage, you could do it per bedroom or per tenant.

Maybe I should have waited til the lease end date and then deducted the gas usage from his security deposit?