How often should all water be changed?

Question
I will be on vacation for two weeks.  I have a one and a two gallon goldfish bowl.  I will give my fancy guppy to someone to take care of.  It won't have a filter or an air stone.  I have kept fish in bowls like that temporarily before.

How often should all the water be changed in the one gallon bowl?  What about in the two gallon bowl?  I am trying to decide which bowl to give the guy so he doesn't have to change the water as much and work as hard, but he'll need to change the water as much as needed.  Thanks.

Answer
Hi,
Honestly, a guppy should be fine with no water changes. the safest thing you can to for a bowl in this situation would be a 10% change every day. it should take about 5 minutes.

use the 2 gallon bowl. more water means toxins will be more diluted and less of an issue.