What do you mean by "warm water?" Measure the temperature of the water and see exactly what the difference in temperature is.

Also, are you planning to pump your water up to your plants? If so, that might help in cooling the water.

Measure the temperature of the water after a few days and compare it to the ambient temperature. You can't really expect it to stay below the air temperature indefinitely.

Pumps make heat and styrofoam will hold it in.

Warm water is bad for roots. You might consider replacing the styrofoam reservoir with a more typical non-insulated plastic box.

@Cole_Robbie

that makes sense on the styro keeping the heat of the pump inside. The reason I opted for styro is because this will be placed outside in the warm weather of tropics. I figured the styro will help keep the sun's heat out.

@tn_gardening

The water is circulating inside the box and not yet going into the plants. Prior to that, the water was cold to the touch. I left it running about 3-4 days and came back to see and the water was warm to the touch. The box was placed inside the house where air temps are fairly stable.

You have the right idea in trying to keep the roots cool.

Burying your reservoir in the ground would be best. You would need to build a drain for the hole, too, so that rain water does not flood it. Second best to the hole would be stacking concrete blocks or big rocks around the reservoir.

Thanks for the suggestion Robbie, I hadn't thought about stacking blocks around the reservoir. I agree burying the tank in the ground would be best, though it's not an option right now :(

I totally agree with "carb", because burying tank in ground would be best option till now. Any suggestion?

You could run an external pump or you can add bottles of frozen water to reduce rez temps or you could run a system that doesn't require continuous running of the pump. those are the basic thoughts I have on how to limit the temps.