A well-mulched sago should not need water outside of the summer growing season.
Sago's normally turn brown from foliar fungus. It can spread pretty fast and is controlled with copper sulate,it does take up to several months to recover as the damaged leaves are a total loss and you have to wait for the new growth to replace it. Nutrition is Florida soils is critical for a deep green color.I feed with Epsom salts, coffee grounds, chelated iron and once or twice a year I add Palm fertilizer with minors. The Cycad family is not a palm at all but they are often referred to as palms and they appreciate the same food. The short story is that healthy growth is all about nutrition,just like in people.The common insect is Asian scale and is often misdiagnosed as a fungus. It can be controlled with an oil spray or you can make a quart of extra coffee and add 1 Tbs of Murphy's Oil soap. Put into pump up sprayer and carefully spray bottom and top of foliage with this solution and it does a perfect job.
If you are seeing what looks like white powder on the leaves before they turn brown then that is probably a good indication you have cycad scale and should follow Garden Rebel's suggestion to use horticultural oil or the Murphy's and coffee combo, making sure to prune off all fronds that show any sign of infestation and disposing of them in a sealed plastic bag.
I have done everything recommended and now have to wait for a little while to see if everything is working
good luck! there's nothing harder than waiting!
Expect a renewed growth and fresh look somtime is the spring,perhaps even mid or late spring.
Patience is one of the hardest things for a gardener to learn.