redearslider.com

I'm planning to get two young RES and am currently unsure on the tank set up.

Water Heater

I understand that a water heater is recommended, however I live in a country near the equator, which means that the temperature here ranges from 23 degrees Celsius (73.4 °F) to 32 degree Celsius (89.6 °F) year round, hence the room temperature is usually around 27 degrees Celsius depending on how hot the day is. In this kind of environment, is there a need for a water heater?

Light/Heat source

Secondly, I have questions about the UVA,UVB and basking lights. Instead of having the lights and heating sources installed, can the tank be placed by the window where it is exposed to the sun rays (direct sunlight only in the morning)? Of course, I plan to have around half of the tank blocked from the sun in case it gets too hot. This way, the RES can bask in the area of the tank where it is exposed to the sun. I would like to know if this set-up is possible.

This is the first time I will be having a RES so I require some advice from the experienced as I want the RES to be able to grow well under my care. Thank you!

If anything have the water heater as a backup, but you can probably skip it. 80F is good for hatchlings.

Keeping the tank near the window is not a good idea. UVB rays are filtered out by the glass and the screen. Sunlight can dramatically warmup a small tank. And lastly, you don't want to expose the turtles to any cold breezes.

If you put your tank by a window your also asking for algae to invade the tank. That and what Steve said.