Go online and look for mobile groomer vehicles - they use recycled water. Their vehicles only carry so much water - and they typically use a hydro system that recurculates the water. I use this system for the vet grooming shop I work for and I have to tell you while it saves him on his water bill the cleanliness of the dogs is comprimised. With the mobile system if you're the first groom of the day - lucky you, then all you have is your dogs dirty water, but if you're the last... Having said that - I have seen some great groomers who own their own mobile vans. I just don't like the hydro system.
When I built my shop I refused to use the hydro system. Clean water for every part of the bath is key to a great groom. The hair doesnt cut or dry well when oily or dirty.
Also ask if the person is experienced or ceritifed. If certified by what authority? Are they members of a grooming organization? Do they attend continuing education classes?
Find a groomer that does one-on-ones where your pets are the only ones in the shop. I never kennel my clients dogs - the have a play area until it's time to groom then once groomed they go in a gated area and when parents come I pop them up on the grooming table and do a final brush out and ask them to comment on the cut. Any changes that need to be made get done. There are some great small shops out there just begging for great clients!
Ask a lot of questions - ask other Yorkie owners who they use?