Misc: What metal are hot water pipes most often made of?

Questions

How many of every four US Federal tax dollars come form individual income taxes?

What was the most common cause of US workplace deaths in 1993?

What explorer first recorded the Polynesian sport of canoe surfing in 1771?

What literary sleuth was originally stuck with the first name Sherrinford?

What kitchen appliance does the typical American open 22 times a day?