A whole house filter generally is installed in line with your incoming water line. The basic whole house filter uses just one filter cartridge and will last a family of 4 about 2 years. The size of water filtration system you choose should depend on the size of your home and the number of bathrooms. Usually a system with a 8-9 gallon per minute (GPM) rating is suitable for a family of up to 5.
If you require specialized filters then you will want to get a double or triple water filter system.
Many people have inquired about a fluoride filter for their shower. While typically people will use the fluoride filter on the refrigerator or countertop filter, this is the only way to filter fluoride from your shower.