This Instructable is a step by step description of the process of adding a sink to the top of a toilet allowing the use of the clean water before it goes into the bowl.

Motivation
Water is a precious resource and our everyday lives are immersed in consuming it. The average toilet uses excessive amounts of water. This hack allows you to minimize some of that water consumption.
I wanted this instructable to be simple enough that anyone could build it with basic tools and materials. I also tried to be material conscious with this project in that: many of the materials are recycled from other things (sheet wood and copper tubing) or second hand (metal bowl), and that it is put together using screws and friction fittings so when the sink has finished serving its purpose it can easily be taken apart and the parts can be recycled.

Step 1: Materials

Materials

9inchx20inch piece of sheet wood
Small plastic funnel
Copper tubing half inch outside diameter
Metal bowl approximately 8 inch diameter
4 feet of Vinyl tubing 1/8 inch inside diameter
4 "L" brackets and small wood screws
Scrap paper
Silicone latex caulking glue
Steel binding wire

Tools
Hand drill
Jig saw
1/2inch spade drill bit
1/8inch drill bit
Center punch
Sharpie
Hole saw 3 inch
Exacto knife

Step 2: Locate the Parts and Trace

Remove the lid from the toilet tank. Locate the over flow tube, gently remove the rubber tube going into the top of it. Take the small plastic funnel and stick it in the tube. Now take a straight edge and span it across the walls of the tank next to the funnel, and mark the edge on the funnel. Now remove the funnel and lay a piece of paper of the tank and trace out the walls and the location of the over flow pipe in relation to them. Next take the lid from the tank and trace it onto the sheet wood.

Step 3: Cut Out the Lid

Cut out the shape of the lid with a jig saw from the wood and clean up as necessary with sand paper. Now take the paper tracing of the tank and cut on inside wall line with scissors. Now center the tracing on the new wood lid, and take the center punch and mark the center of over flow tube on the wood lid. Using this mark as center drill a 3 inch diameter hole with the hole saw.

Step 4: Making the Sink

With a marker extend the line on the funnel so that it goes all the way around, cut on the line with an Exacto knife. Now take the metal bowl and create drain holes in the center with a small drill bit, making sure the final drain is no bigger than the top of the freshly cut funnel. Next place the funnel on the bottom of the metal bowl and apply liberal amounts of caulking glue on the crack between the bowl and funnel.

Step 5: Faucet

The faucet is made from copper tubing bent into an upside down "J". To bend the tubing without kinking it, tightly wrap the wire around the section to be bent and carefully bend it with your hands, retightening the wire occasionally. Trim off the extra tubing with a tubing cutter. Drill a half inch hole with a spade bit, 3 inches away from the large hole in the wood lid. Force the long end of the copper "J" into the hole, friction should hold it in place.

Step 6: Bracket in Place

To keep the wood lid from sliding around on the tank you can attach brackets. To figure out where the brackets need to be, flip over the lid and center the paper tracing of the tank on it. The brackets should be against the outer edge and attach with small wood screws.

Step 7: Installation

Back inside the toilet tank locate the rubber tube that was inside the over flow tube and follow it back to the float valve, and pull it off. Now attach the 4 foot vinyl tubing. Push the other end of the vinyl tube through the bottom of the wood lid half inch hole and up though the copper tube until just before it sticks out the other end of the copper tube.
Now lower the new lid onto the tank making sure the vinyl tubing does not interfere with the internal mechanisms in the tank. Take the metal bowl with the funnel attached and make sure the glue is dry. Now look down the 3 inch hole in the lid and you should see the over flow tube. Take the bowl and funnel and lower it onto the hole, the funnel needs to go into the over flow tube.

Step 8: Finished

The sink is now complete.
I would recommend putting some kind of water proofing on the lid to protect the wood.
Check out the video of the sink in action.
Thanks for viewing my instructable.