Definitely get a traffic lawyer to represent you here.
That said, if he didn't cite you for speeding...then you were not only not speeding, you were going under the speeding limit. He can't possibly say in court you were speeding at the time because it would be somewhat of a contradiction to not having cited you for it. So you can run with that.
As for failing to maintain the vehicle, that's very weak in itself imo. If you couldn't see the puddle in advance, and couldn't have known the depth of it and impact it would have, then its not fair to be cited for the outcome when you surprisingly encountered it. That's perhaps like saying anytime you lose control of your car, you're at fault because you're going to fast to avoid it, and that's simply not the case.
So from your perspective, you could have been going 1/2 as fast and the water puddle/depth would still have been unavoidable because it was very inconspicuous and deceptively deep, and much unlike the conditions of the road surface that you had been driving on before the crash. Sure it was raining, but your tires are in excellent condition and you were being cautious given the ability for your car to handle rain as well as the highway's ability to direct rain runoff away from the lanes.
Anyhow, that's my primitive thoughts about weasiling out of it.