I didnt bargain and my water is 35 baht per unit !! In dry season the maintenance people water the gardens daily and that was using 100 cubes or so a month !!!
Exact government rates are listed here
http://www.aseanenergy.org/download/...ity_Tariff.pdf
Or Googled in HTML here
http://216.239.53.104/search?q=cache...es+kwh &hl=en
Certainly 5 baht is high and he is nearly doubling his money on you for low usage.. Problem my area has is that it was classed as a business are (the development) and as such is charged Biz rates at 3.6 baht per unit..
15 baht per cube might need some pumping costs attached.. How they source thier water (well / Artisan bore / Gov water) would all have an impact.. Mine is expensive but I have someone to shout at if the water drys up (as it did a few months back) he was then getting water trucks up daily at >150 baht per cube...