Start with water as your baby may spill a fair amount at first. Obviously, if the baby is to be taking a fair amount of a variety of foods by 6 months of age, he may need to be started on solids by 5 months of age. However, some babies prefer to wait for the mother in order to drink something. But getting the baby to take a bottle surely won't hurt. Not necessarily true.
Some babies do fine with both.
The occasional bottle, when breastfeeding is going well, will not hurt. But if the baby is getting several bottles a day on a regular basis, and, in addition, your milk supply decreases because the baby is nursing less, it is quite possible that the baby will start refusing the breast, even if he is older than 6 months of age. Babies need to drink milk when the mother is not at home. Three or four good nursings during a 24 hour period plus a variety of solid foods gives the baby all he needs, nutritionally, and thus he does not need any other type of milk when you are at your outside job. Of course, solid foods can be mixed with expressed milk or other milk, but this is not necessary.