The bath water definitely should be changed every day but if you’re going out of town for the weekend, having that in cage bird bath for more water is handy. Just make sure you clean it first and then sterilize it with either hydrogen peroxide (which decomposed into water) or rubbing alcohol. WARNING: If you use rubbing alcohol you MUST RINSE it thoroughly before you put it back and never expose the bird to the liquid or the fumes. And since, if you’re heading out of town, this will probably be a trip you would have planned, go and get a $0.79 gallon of distilled water to put into the bath before you leave. This is also good for regular fish, betta fish, ironing and even emergencies having a gallon of distilled water around. You can use unopened spring water too but this really helps stifle the growth of microbes right off the bat especially if you think ahead and put it in the fridge the day before. Worst case scenario you have some clean drinking water before it expires so it will never really go to waste. Even so… $0.79? C’mon.
Having done those simple things can allow you some leeway in special circumstances. Using clean, cold water you can leave on Friday, come back Sunday and be pretty confident that the water will be OK. The only caveat to this is that if you get your bird as a baby, make sure they learn to drink form the water silo first, THEN slowly add the bath to the cage setup. That way they’ll drink from the silo more often than the bath even with both in the cage. They’ll still drink from the bath but this way they’ll do so less. And make sure you clean the cage before you leave for a weekend trip. Wingy flaps can fling dust and food and feathers and paper shreds and everything in between up in to the air and into the bath water so clean this prior to leaving or you’re GOING to come back to a sludge pool. Some birds insist on pooping in their bath, others don’t. No rhyme nor reason, but… if you CAN have someone come in on Saturday and give them fresh water that is certainly preferable since we all have neighbors and it takes literally less than 5 minutes but let’s face it… life happens. However, this way you can at least give your bird the best chance of staying healthy.