I think the main problem with addressing such issues is due to the approach. If you come straight out and criticize what a person is doing or isn't doing, then you put them in a defensive position only to be met with opposition. I think the better approach is to take an interest in what they are doing and trying to understand why it is they are doing what they do. Only then can you try and understand what approach if applicable can be applied to that particular situation. For example:
owner: "We only use distilled water for our animals."
customer: " Is there any particular reason, is normal water bad?"
owner: "Yes, normal water can have additives that can cause all sorts of problems."
customer: "Oh, that's interesting. I'll have to research that as it's been my understanding from reading <insert literature, web sites> such as <insert title> that distilled water can be problematic because it's missing trace elements which are essential to the well being of animals. But thanks for your information, I'll definitely do some more research to try and understand what is better to use."
Now, this sample conversation can obviously go many different ways, but the key is not to create an argument or make accusations, the key is to plant the seed of knowledge and hope it takes from there. Believe it or not, there are people out there that do want to do things right, they just can't handle criticism and tend to stick to their guns just for the sake of being stubborn when told what to do. But if you are non-confrontational and take a sincere interest in what they do and why, then hopefully you can inject some of your own wisdom in a well received manner and give them the opportunity to figure it out on their own (which is how some people like to do things anyways rather than being told).
And of course there are those other people that could care less regardless of your approach. It's best just to stay away from those people/places and if they are keeping their animals in conditions that are severely detrimental to the animals well being, then I believe we all have an obligation to report them to the proper authorities anonymously.