• Here is a link to a free article on the topic: "What type of Water Should I use for HPLC, UHPLC or LC/MS Analysis?"; https://hplctips.blogspot.com/2013/10/what-type-of-water-should-i-use-for.html

Just use a high quality RO water system with final stage filtering ("polishing") for LC-MS analysis (brand is less important, quality matters more). Costs, while important for supplies such as water, should not be the #1 consideration. The quality of the mobile phase is VERY important as the quality of the data obtained from any methods used is limited by the quality of the chemicals and additives used. Saving money on consumables such as solvents, columns and supplies is a mistake. Note: The sales people will always tell you their product is "the best", so do not rely on brochures or sales advice. You can always send out samples of the water for formal testing to check the properties that matter most for your application. Just factor the cost of consumables into the budget.

When doing research in many SAIF labs it is commonly used (MilliQ-models) and proven results with better health of instrument. If you are planning to buy it for your laboratory, I refer to any advance /latest models of milliQ.

Addition information I will provide in some time with real user's reviews.

Thank you William Letter and Desh Deepak A P Singh Chauhan for your replies. I totally agree that trading quality for money is never a good option LC-MS/MS analysis and sample prep. I just cannot say if the water from the Evoqua has any risk of being of lower quality. On paper, it doesn't. But I don't have the time to try to get water samples, etc. In the neighbour lab we have an older MilliQ system, and I was told that it is very robust over the years. That's the type of info that I cannot get for the Evoqua system because no one that I know used one for long enough. Also MilliQ can deal with much lower feed water pressure, which is important in countries were water and electricity are not always super consistent.

Since we have this MilliQ older system using the same consumables, I'll probably go for the MilliQ so that we can share consumables if needed, and then I'm also sure it is compatible with ISO accreditation, etc. (the distributor of the Evoqua didn't have answers regarding use in clinical diagnostics...)

Sounds like a reasonable plan. You should be fine.

Thanks for mentioning here so I get the update. Yes as in Research, every time we have to mention the instrument when we write articles, Research papers or thesis. If someone already mentioned instrument alike your in high impact journal then it is common to go with the flow.