Yes. It is rated 5 ATM (50 m), which covers swimming and showering. Avoid pressing the buttons underwater.

Does it have a countdown timer?

No. It has an alarm, stopwatch, world time and date, but no countdown timer.

What battery does it use?

A CR2025 cell. It is a common battery, so replacement is cheap and easy.

Is the glass really sapphire?

The listed spec says sapphire, which is unusual at this price and resists scratches well. Treat that claim with some caution, since most Casio watches in this range use mineral or acrylic glass.

How big is it on the wrist?

It is a compact resin case at about 1.1 oz, so it wears small and light. It suits narrow wrists better than large chunky watches.

Is the Casio W-96H-1AV worth it?

It is a solid basic digital watch. Similar Casio digitals often offer more functions, so weigh its light weight and sapphire glass against the missing timer and dim light.