Anybody been through the process of getting subsidies/rebates/credits for energy efficient appliances in Houston?

Like most, I'll be replacing a water heater. I've seen some manufactures rebates which amount to a 5% – 10% mail in rebate. Those rebates seem to be independent of their efficiency and more tied to their cost. Curious if anyone has gone through getting any type of city rebate or maybe federal tax credit during tax time. I suspect some sort of proof of purchase and/or installation would be required, and have to meet some efficiency criteria. I'm trying to do the "yea but if I spend a couple hundred more to get this model, i'll ultimately get back x dollars" algebra. Thanks for the help, stay safe and stay warm!