Is PVC Schedule 40 pipe safe to use in a potable water supply?
You should not worry about health. Most schedule 40 PVC is National Sanitation Foundation (NSF) rated for potable water, and it's likely that yours is. Do you see "NSF" printed on the pipe? Even if it isn't, I wouldn't worry about toxicity. The problem with PVC pipe is that it may have issues with leaks. It will degrade when exposed to UV light (such as sunlight), and also high temperature. Its pressure rating is to be derated at high temperatures. Because of this, PVC is not approved for use in houses for potable water.

There are many websites stating that PVC is both safe and unsafe. The trend that I see on the more scientific sites is that some of the chemicals used in PVC decades ago are unsafe, and also some of the plasticizers are also somewhat toxic (similar to the PBA toxicity scare a few years ago). But if your pipes are years old, most of what will leach out already has. Also, you can follow the advice which is given about houses with lead in their water system: Don't drink the hot water, and let the cold water run for a minute until it gets cold before using it.

Back to the real issue with PVC... its reliability with respect to hot water: Let's say that your hot water is at 140 F.... We can use a derating chart for PVC to find its actual pressure rating at higher temperatures. Based on the chart, multiply the 73 degree pressure rating by 0.22 to get 106 PSI. Although this is above the desired water pressure of 60 PSI, 106 PSI is not unheard of. Also, keep in mind that your hot water might be above this temperature, so the actual maximum pressure may be lower.

The solution is to replace your pipes with an approved material such as CPVC (a stronger type of PVC), PEX, or copper. All of these are considered safe for potable water (by the government and standards bodies), though one can find claims online of all of them being toxic.