(d) an adequate supply of potable drinking water is provided and maintained at suitable points conveniently accessible to all employees, The employer is required to provide an adequate supply of wholesome drinking water at locations within the workplace that are accessible to employees. The number of locations would be dependent upon the size of the workplace, the number of persons employed, the nature of the work and any requirement for the employee to remain at the workstation for sustained periods. From the HSA Safety, Health and Welfare at Work regulations, page 27, Regulation (d) and (e)... You'd have to make the argument that considering you are required to be at the till for the duration of your shift, your access to an adequate supply of wholesome drinking water can only served by a bottle, or the right to go to the kitchen during your shift. It sounds like you haven't worked hard enough to understand that most people need water on their shifts.