There are ways to treat the ...

There are ways to treat the water so that blow-down is not required!  Extreme softening of ground or surface fresh water, or even seawater (with at least some level of desalination) will leave behind one key ingredient - silica (both the reactive silica, and "polymerized" silica that is un-reactive to molybdate). It turns out that when silica approaches and exceeds a critical residual concentration of above 100 ppm, nearer 200 ppm, this becomes the ultimate corrosion inhibitor known to mankind.  Corrosion rates such as 0.01-0.001 mpy (mils per year) were reported in NACE for this.

There are a number of ways to arrive at the water condition:

(1) high efficiency softeners (sodium ion exchange, counter current, special bed geometry

(2) Nanofiltration with back addition of small amounts of silicates

(3) membrane capacitive deionization (perhaps this will be best especially for seawater source water, since it removes salt along with hardness, is tunable as to deionization extent, and to recovery fraction, is very robust (tolerant of chlorine), is very easily scaled up to vast arrays, and has the lowest specific energy input of any water purification system.  mCapDI does not remove silica.