How can distillation be used to prepare pure water from tap water?

so what should i write then

As I read the question, it isn't asking you to tell what distinguishes distilled water from some other kind of water or which is more common. The question is asking you to describe the PROCESS for purifying water by using distillation. If you read the link I gave you AND go to google and type in some phrases you can find a picture, I'm sure, of a still. Then you will know how it works. Here is a different site that may explain it a little better than the former one.

http://www.chemhelper.com/distillation.html

Distillation is a process that can be used to purify water by separating it from impurities. Here's how you can use distillation to prepare pure water from tap water:

Materials needed:
1. Tap water
2. Distillation apparatus (such as a distillation flask, condenser, and collection container)

Procedure:
1. Start by pouring tap water into the distillation flask. Make sure not to fill it more than two-thirds full to allow enough space for vapor formation.
2. Connect the distillation flask to the condenser. The condenser is a tube that cools down and condenses the water vapor produced during distillation.
3. Set up the collection container to collect the pure water that is obtained.
4. Apply heat to the distillation flask to boil the tap water. The heat source could be a Bunsen burner or an electric heating mantle.
5. As the water boils, steam vapor will rise and enter the condenser. The condenser cools down the vapor, causing it to condense back into liquid form.
6. The condensed water droplets collect at the end of the condenser and are collected in the collection container. This water is the purified water, free from most impurities present in tap water.
7. Continue the process until you have collected the desired amount of pure water.

The distillation process separates the pure water from impurities like minerals, dissolved solids, and contaminants that have a higher boiling point than water. The boiling water vaporizes and leaves behind these impurities, which do not evaporate in the same way. As a result, the condensed water obtained in the collection container is purer and closer to being chemically pure.

Keep in mind that while distillation is an effective method to purify water, it might not remove certain volatile organic compounds or gases with lower boiling points. Additionally, distilled water lacks minerals and other beneficial elements found in natural water sources, so it may not be suitable for long-term consumption without supplementing essential minerals.

http://en.wikipedia.org/wiki/Distilled_water

You may be able to go to www.google.com and type in different phrases and come up with a picture of a still used for distillation of water.

Distilled water is the most common form of purified water.

anything else

I'm not sure distilled was is the most common anymore. It was at one time but I suspect deionized water now is the most common, especially for laboratory work.