Can I use copper pipes to supply my DI water?
Copper pipes is not recommended because as shown earlier where DI water is hungry, over a period of time, the deionized water will corrode those pipes. What would be sufficient to plumb or to use piping on your DI system will CPBC plastic.
What is a good way to monitor my DI water’s resistivity?
The simplest way is from the supplier of the DI water columns themselves, many of them will have at the last tank on the output will be a simple what we call “go no-go” red and green light, those are set typically for either 2 megaohm or 1 megaohm. You can even get some with lower rating too down to the k-ohm if need be. If there are other requirements, there are portable instruments available from companies like Myron L that has monitoring systems.
What is the temperature limit or the best temperature for DI water?
You ideally want to run it as hot as practical, but you are limited by, especially if you close lube your rinse station where that water will go back in through those resin beds, you are limited by the supplier of those resin beds and typically the limit will be 125°F.