Powdered formula is not sterile, it can and frequently is contaminated with disease causing bacteria before you even open it. For this reason it is NOT safe to mix it with hot tap water.
Nor is it safe to use hot tap water to mix any formula because hot water heaters can contain many contaminants at high levels such as lead because the water evapourates and heavy metals build up.
Liquid formula (ready to eat and concentrate) is contaminated with BPA because the can linings contain BPA which leeches into the formula when it is heat sterilized. I don't believe that any formula companies have replaced the can linings with BPA free linings as of yet.
http://www.infactcanada.ca/Newsletters/2007-Winter/safety_guidlines.htm
E. sakazakii is a highly virulent bacteria which is resistant to the high-temperature processing methods used in food production. If infants, especially those who are newborn, low-birthweight or premature, are infected with E. sakazakii, it can cause meningitis, necrotizing entercolitis, and sepsis, and is potentially fatal. As a result of reports of baby deaths from E. sakazakii contamination in recent years the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) have declared this a significant public health hazard and have convened two expert meetings on the issue: one in 2004 and more recently in January of 2006. After reviewing the scientific evidence the 2006 meeting produced a report noting that both manufacturers and governments must act to reduce the health risks associated with the intrinsic contamination by E. sakazakii. Studies reviewed by the meeting noted that up to 14 per cent of formula packages may be contaminated by the bacteria.
http://www.who.int/foodsafety/publications/micro/pif_guidelines.pdf
Powdered infant formula (PIF) has been associated with serious illness and death in infants due to infections
with Enterobacter sakazakii. During production, PIF can become contaminated with harmful bacteria, such as
Enterobacter sakazakii and Salmonella enterica. This is because, using current manufacturing technology, it is
not feasible to produce sterile PIF. During the preparation of PIF, inappropriate handling practices can exacerbate
the problem
[...]
In general, sterile liquid infant formula is recommended for infants at the highest risk of infection. Where sterile
liquid infant formula is not available, preparation of PIF with water at a temperature of no less than 70 °C
dramatically reduces the risk. Minimizing the time from preparation to consumption also reduces the risk, as
does storage of prepared feed at temperatures no higher than 5 °C.
Users of PIF are made aware that powdered infant formula is not a sterile product and may be contaminated
with pathogens that can cause serious illness. Correct preparation and handling of PIF reduces the risk of illness.
http://www.akwater.com/operations_faq.shtml#babyformula
Q: Is it okay to use hot water from the tap to make baby formula?
A: No. Hot water may contain impurities that come from the hot water heater and plumbing in your house. To avoid this, use cold water and let the water run for a couple of minutes before you use it if that tap has not been used for a while, overnight, or all day. You can then heat this water on the stove. Catching the water you flush out of the tap in a container and saving it for plant watering is a good conservation measure.
http://www.dcwasa.com/waterquality/faqs.cfm
Is it okay to use water from the hot water tap for drinking, cooking, or making baby formula?
Hot water generally comes from a hot water heater that may contain impurities that should not be ingested. Some of these impurities might be metals from household plumbing that are concentrated in the heating process. Additionally, these impurities from the household plumbing dissolve more rapidly in hot water than cold water causing the amount of impurities to be higher in hot water. Therefore, cold water should be used for all drinking and cooking uses, as well as for baby formula.
http://www.ewg.org/newsrelease/Infant-Formula-Makers-and-Canned-Food-Producers-Called-On-To-Remove-BPA
“Liquid formula is the biggest culprit in exposing infants to a toxic hormone-disrupting chemical, but kid-friendly foods like canned chicken noodle soup and ravioli also have high levels of BPA,” said EWG Senior Analyst Sonya Lunder. “BPA was initially used as a sex hormone. It should never have been allowed to come into contact with infant formula.”
http://www.theattachedparent.com/21/bpa-the-danger-lurking-in-baby-bottles-formula-cans-and-sippy-cups/
Breastfeeding would reduce or even eliminate the need for bottles or formula and subsequent exposure to BPA. For parents that need to use formula though it is hard to find companies that are not using BPA to line their cans of powered or liquid formula. A new study from the Environmental Working Group has discovered that 4 out of