Round Rock Texas Water Questions

I have recently gotten into All Grain brewing (BIAB) and have been trying to read up on water chemistry. Below is a link to the latest published water quality report for my city:

http://www.roundrocktexas.gov/docs/ccr_2011_final.pdf

I know we have very hard water here. Would it be easier for me to buy 100% RO water and adjust following the water chemistry primer guidelines, or can I dillute my tap water with a certain level of RO water and achieve successful results. My first few all grain batches I have used 5 gallons of RO water with approximately 2-2.5 gallons of tap water...but I am not sure that gets me to optimal levels. I routinely brew IPAs and Pale ales, with some stouts/porters too. Thanks in advance for the help!

If you can get RO cheaply, then yes I'd use that. Your water could have a lot of the hardness and alkalinity removed with slaked lime, if you wanted to try that, but it may be more trouble than it's worth for you (and you'd still likely need to treat your water with acid in the mash).

It has modest concentrations of the flavor ions: Na, Mg, SO4, and Cl. The big problem is the alkalinity and calcium levels. In addition, the water source varies between surface water and groundwater. Without knowing where they are drawing from, it would be difficult to estimate what your tap water quality was. There are inexpensive aquarium test kits for Ca and alkalinity that could allow you to have a good idea of those levels. But is that testing and effort worth it to you? If it is, then a combination of RO dilution and acidification could provide good brewing water. If you just want to get on with it, then starting with RO water could be the easiest.

Thanks for the replies! So if I use 5 gallons of RO water and 2.5 gallons of tap water, that will still not dillute enough to be optimal on the alkalinity and calcium levels? I am leaning towards using 100% RO and then doing the baseline recommendations following the water chemistry primer. I can get 5 gallons for $1.35 at the local grocery store, so that doesn't add too much cost.