What kind of bananas do you have and what zone do you live in?

If the spots only develop on newly unfurled leaves and the spots don't gradually increase in size, it probably is from sunscald or from the drying action of low humidity wind.

As Wally says, it hard to tell without seeing the plant. They are heavy feeders, and yellowing MAY indicate a lot of conditions. Possible mineral or nitrogen deficiencies, wind damages, improper watering (too much or too little) - all could be the culprit. I have a number of varieties that have red blotches but these are part of their natural coloration. I added a link to the CRFG fruit facts banana page with information on these... Here is a link that might be useful: CRFG Banana page

Only cut back on water if temperatures are below 60 degrees and you are trying to send the plant into dormancy. In that case the plant stops growing, enters hibernation mode and is fine with almost no water for up to 7 months. If you cut back on water but keep it warm and well-lit however, the plant doesn't get the signal to go to sleep and still struggles to grow but without enough water cannot maintain its older leaves anymore. This is because what water it does have is sent to the more important new growth and there isn't enough to go around.