The Condensate lost is ...

The Condensate lost is costly in terms of extra load on the deaerating feed-water tank system, and since it contains heat above ambient temperature, the heat BTU value is also lost.  Over time this can add up to thousands, or even hundreds of thousands of dollars depending on the size of the boiler, and the degree of loss (%), not to mention any damage to steam cycle equipment.

The makeup system will become heavily taxed to keep up, depending on design parameters, especially if the system was designed with 95% condensate return or better in mind.

This extra cost of make-up water to the boiler involves several factors: (1) the cost of water intake, (2) the energy of pumping this water including transfer pumps, R.O. pressure booster pumps, and any electrical power consumed by such devices as membrane capacitive deionization, EDR, CEDI, and or vapor compression stills, and (3) last but not least necessarily are chemical costs and expendable items such as cartridge filters, RO membranes, CEDI stacks, EDR stacks, new ion exchange resin, etc.