I have a washing machine which uses the only available water valve where it is. I want to add a dish washer. However, there is only one water valve. Is it possible to install an accessory so that I get two independent current of water, one for the dish washer and one for the washing machine?
Depending on the size and type of the existing pipe the easiest, simplest way to split the water supply line is to connect a dual shut off valve like this: http://www.amazon.com/gp/product/B002M1S0UM?keywords=dual%20shut%20off%20valve&qid=1446490458&ref_=sr_1_1&sr=8-1. I believe the washer will need a minimum connection size of 3/4 inch hose thread on the valve and the dishwasher hose should be a 1/2 inch pipe thread on the valve. If you have a copper supply pipe you will need to determine the size (usually 1/2 inch) and the fitting (usually male thread) and purchase a valve with the appropriate connections.
You can get a "Y" adapter for a water hose connection like this one:
Image from this Amazon product.
Additional fittings could be used if your dishwasher needs something other than water hose threads. When selecting a splitter such as this, try to find one that is solid brass and labeled for use with hot water. Valves that contain plastic may not be rated for hot water, so be very careful with them.