Drinking water on a hot day:
what two systems are involved in this process?
how are they involved?

When you drink water on a hot day, you use the systems: excretory (Our liquid waste is excreted efficiently as urine through the work of the kidneys, ureters, bladder, and urethra.), circulatory (The heart and blood vessels, which include arteries and veins, circulate blood throughout the body, bringing oxygen to every cell and taking away the carbon dioxide), and the digestive system (The mouth, esophagus, stomach, intestines, and rectum form an efficient pathway for food so we can retrieve the nutrients we need and excrete the rest as solid waste). So, when you drink water, the water flows down the digestive track, help the kidneys and flows to the bladder, and the water reaches all the cells in the body.

I hope this helps! 

That is true! many fish species traveled to the u.s. because of it.