Important! Before you drill, be sure to check the underside of the sink so you won't be drilling into a brace or other obstruction that would make installation of the faucet difficult or impossible.
Faucets require a hole in the sink or countertop for installation.
Faucet installation details will vary depending on the specific manufacturer and model, the following advice applies to our Tomlinson brand faucets and *most* of the generic RO and drinking water filter faucets we have encountered.
Most standard (non-air-gap) faucets, with or without tubing attached, need a hole that's 7/8" in diameter to 1-1/8". You can install most standard faucets comfortably in holes up to 1-1/8".
If you have an existing hole that's slightly larger, you'll need to find an oversized escutcheon to take up the slack. Try a local hardware or plumbing supply store.
If you have an existing hole that's too small, there is no remedy other than to drill it larger. (We loaned our hole stretcher to a customer who did not return it.)
Drilling smaller holes in a stainless steel sink is usually quite easy. A 1/2" hole, for example, can be drilled with a standard metal bit from the hardware store. It's easiest to drill a small pilot hole, then follow with a 7/16" or 1/2" bit. The cone-shaped “Unibits” that drill an increasingly larger hole work great on stainless sinks. Larger holes are difficult in stainless. In hardware-store quality tools, a good sharp “hole saw” is your best choice.
Many of the new sinks that appear to be porcelain are actually quite thin and quite easy to drill with a standard masonry drill bit. If in doubt, consult the sink manufacturer for advice.
Drilling older porcelain or cast iron sinks should probably not be attempted unless you have special equipment (a Relton Sink Cutter, for example).
Tip #1: If there is simply no place to drill a hole in a sink, you can sometimes drill into the countertop next to the sink.
Tip #2: If you're buying a new sink, you can usually get the seller to furnish a sink with the hole you need.
(whole house & well units)