Tank or tankless under-sink RO: how should you compare them?

Measure the space you actually have

Photograph the cabinet, drain, shutoff and electrical outlets. Note any disposal, pull-out drawer or stored items that occupy the space. Ask the installer for the installed dimensions and future access needed to change filters or the membrane.

A storage tank changes how much water is available at once. A tankless design may use a pump or electricity and has its own output rating. Ask for the conditions behind each number before comparing brochures.

Compare the same daily routine

Estimate how many bottles, cooking pots and refrigerator connections you want to fill. Ask each seller how the faucet behaves after several draws and what happens during a power outage. Get the faucet, drain connection and optional refrigerator line shown in the quote.

EPA notes that point-of-use RO models differ in water efficiency. Compare the exact model’s waste-to-treated-water ratio and any WaterSense label, not just a ‘low waste’ phrase.

Reference: EPA WaterSense point-of-use RO

Price the years after installation

Put prefilters, postfilters, membrane, tank or pump service and any proprietary cartridges in one comparison. Ask whether the exact unit carries certified claims for the concern in your water.

A practical choice is the system that fits the home and is straightforward to maintain, not the one with the most dramatic product name.