You will probably be just fine using water of that quality. However, if the system is supposed to be outputting water of 18 MOhms and is only providing water of 8 MOhms, then this tells us that something is wrong with the water system (probably time to replace one or more of the water cartridges. Also time to check the incoming water supply for problems too). These water systems require regular maintenance.

A related article for those interested:

"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

For HPLC is required ultrapure water with high resistivity (>18.0 MΩ.cm) and free from particulates not only for obtain a high resolution but to avoid damage on pump and injector, and avoid obstruction of column and frits. As William comments, it would be neccessary to replace the cartridges to ensure a better HPLC performance.

Thank you very much all for the information!!

Yes, you can use for HPLC.

William Letter gave good information. I would only add the advice of running blanks to ascertain the location of ghost peaks, but one should run those anyway even if the water system is working perfectly.

Yes, can be use but preferably better better when the resistivity is 18