What type of water filter is the easiest to use to treat water for drinking?

• portable water filter
  A portable water filter is a safe and inexpensive way to treat water for drinking, and a good one can cost less than $100.
• membrane water filter
  A portable water filter is a safe and inexpensive way to treat water for drinking, and a good one can cost less than $100.
• plastic water filter
  A portable water filter is a safe and inexpensive way to treat water for drinking, and a good one can cost less than $100.