Is MilliQ and Millipore water nuclease free? - (Sep/18/2008 )
when I am going to do PCR, is it necessary to autoclave the water? Since I do not think autoclave can remove the nuclease efficiently.
I do not think that it is certified to be free of nucleases, however, if cartridge is not contaminated with microbes there will be no real source for nucleases;
to become sure we use sterilized Milli Q water for molecular biology
but sterilising will not remove nucleases, bearer.
That said, for most applications and provided (as bearer said) there is no contamination in your unit, you should be ok using milli-Q water (don't think I would though)
what about getting some DEPC to treat your water with??
well, there are some milliQ water companies claimed that it is free with nuclease. Of course better be safe than sorry. I always use autoclaved milliQ.
But autoclavation means nothing to PCR here since it is not able to remove nuclease, if there are already some in the MilliQ water. And it can not remove the contaminated bacterial DNA either, is it?
Autoclaving will remove DNase. Back in the good old days, when men were real men, women were real women, small furry creatures from Alpha Centauri were real small furry creatures from Alpha Centauri, and you had to clean up your own reagents, boiling RNase was the standard way to get rid of any DNase that hung around. Have a look at an old copy of Maniatis, or Sambrook.
Apart from that, there are a number of grades of MilliQ filters, for different requirements.
I always autoclave distillled water or miliQ.
just to be safe then sorry.
That said, for most applications and provided (as bearer said) there is no contamination in your unit, you should be ok using milli-Q water (don't think I would though)
what about getting some DEPC to treat your water with??
sterilizing by autoclaving (as swanny suggested) to be precise; you are right, DEPC water is a good alternative...
sorry bearer, i misunderstood you there 
For PCR, RT, QPCR use a certify nuclease free water (is more expensive, but you are sure what you are adding. For all RNA assays I prepare ultra-pure water with DEPC (1mL DEPC/L leave stirring for at least 1 hour some keep it overnight but the media life of DEPC in water is 30 min so keep for more than 2 h will not do a difference and autoclave for 45 min. I used to clean the equipment for rna assays and to prepare MOPS buffer.