A drinking water system is a RO unit with an in-line carbon filter as the post filter to remove any abnormal tastes or odors. It normally comes with a pressurized storage tank and a RO faucet. They reduce the TDS down low enough for safe drinking water levels, but are not completely free of TDS. Reefkeepers (discussed in the next FAQ) are RODI systems and provide -0- TDS water. Reefkeeping units do not come with any tank or faucet.