Below is a comprehensive list of impurities found in tap water.
Most of these impurities can be removed with a good quality water filter.
Acenaphthene
Acenaphthylene
Acetochlor
Acetone
Acrylonitrile
Alachlor (Lasso)
Aldicarb
Aldicarb sulfone
Aldicarb sulfoxide
Aldrin
Alpha Chlordane
Alpha particle activity
Alpha particle activity (excl radon and uranium)
Alpha particle activity (incl. radon & uranium)
Alpha particle activity (suspended)
alpha-Lindane
Aluminum
Ammonia
Aniline
Anthracene
Antimony (total)
Aroclor 1016
Aroclor 1221
Aroclor 1232
Aroclor 1242
Aroclor 1248
Aroclor 1254
Aroclor 1260
Arsenic (total)
Asbestos
Atrazine
Barium (total)
Baygon (Propoxur)
Bentazon (Basagran)
Benzene
Benzo[a]anthracene
Benzo[a]pyrene
Benzo[b]fluoranthene
Benzo[b]fluoranthene & Benzo[k]fluoranthene
Benzo[g,h,i]perylene
Benzo[k]fluoranthene
Beryllium (total)
beta-Lindane
Bromacil
Bromate
Bromide
Bromobenzene
Bromochloroacetic acid
Bromochloromethane
Bromodichloroacetic acid
Bromodichloromethane
Bromoform
Bromomethane
Butachlor
Butyl Acetate
Butyl Benzylphthalate
Butylate (Sutan)
Cadmium (total)
Carbaryl
Carbofuran
Carbon disulfide
Carbon tetrachloride
Chloramben
Chloramine
Chlorate
Chlordane
Chlorine dioxide
Chlorite
Chlorodibromoacetic acid
Chloroethane
Chloroform
Chloromethane
Chloropicrin
Chloropropane (DBCP)
Chromium (hexavalent)
Chromium (total)
Chrysene
cis-1,2-Dichloroethylene
Combined Radium (-226 & -228)
Combined Uranium (mg/L)
Combined Uranium (pCi/L)
Copper
Cyanazine (Bladex)
Cyanide
Dacthal
Dalapon
Desethylatrazine
Desisopropylatrazine
Di(2-Ethylhexyl) adipate
Di(2-ethylhexyl) phthalate
Dibenz[a,h]anthracene
Dibromoacetic acid
Dibromochloromethane
Dibromoethylene
Dibromomethane
Dicamba
Dichloroacetic acid
Dichloroacetonitrile
Dichlorodifluoromethane
Dichloroethane
Dichloroethane
Dichloroethylene
Dichlorofluoromethane
Dichloroiodomethane
Dichloromethane (methylene chloride)
Dichloropropane
Dichloropropane
Dichloropropane
Dichloropropanone
Dichloropropene
Dichloropropene
Dichlorprop
Dieldrin
Diethylphthalate
Dimethylphthalate
Di-n-butylphthalate
Dinitrotoluene
Dinoseb
Dioxane
Diquat
Diuron
Endosulfan I
Endothall
Endrin
EPTC (Eptam)
Ethion
Ethyl ether
Ethylbenzene
Ethylene dibromide (EDB)
Ethyl-t-butyl ether (ETBE)
Fluoranthene
Fluorene
Foaming agents (surfactants)
Formaldehyde
Glyoxal
Glyphosate
Gross beta particle & photon emitters (man-made)
Gross beta particle activity (dissolved)
Gross beta particle activity (mrem/yr)
Gross beta particle activity (pCi/L)
Gross beta particle activity (suspended)
Heptachlor
Heptachlor epoxide
Hexachlorobenzene (HCB)
Hexachlorobutadiene
Hexachlorocyclopentadiene
Hexanone
Hydrogen sulfide
Hydroxycarbofuran
Indeno[1,2,3-cd]pyrene
Iodomethane
Isophorone
Isopropyl alcohol
Isopropyl ether
Isopropylbenzene
Lead (total)
Lindane
Lithium
m- & p- Xylene
Manganese
Manganese-54
MBAS
m-Dichlorobenzene
Mercury (total inorganic)
Methiocarb
Methomyl
Methoxychlor
Methyl ethyl ketone
Methyl isobutyl ketone
Methyl methacrylate
Metolachlor
Metribuzin
Molinate (Ordram)
Molybdenum
Monobromoacetic acid
Monochloroacetic acid
Monochlorobenzene (Chlorobenzene)
MTBE
m-Xylene
Naphthalene
n-Butylbenzene
n-Hexane
Nitrate
Nitrate & nitrite
Nitrite
Nitrobenzene
Nitropropane
n-Nitrosodiphenylamine
n-Propylbenzene
o-Chlorotoluene
o-Dichlorobenzene
Oil & Grease (total)
Orthophosphate
Oxamyl (Vydate)
o-Xylene
p,p’-DDT
Paraquat
p-Chlorotoluene
p-Dichlorobenzene
Pentachlorophenol
Perchlorate
Phenanthrene
Phenols
Phosphate
Phosphorus
Picloram
p-Isopropyltoluene
Potassium-40 (total)
Prometon (2,4-bis -6-(isopropylamino))
Propachlor
p-Xylene
Pyrene
Radium-226
Radium-228
Radon
sec-Butylbenzene
Selenium (total)
Silver (total)
Simazine
Strontium
Strontium-90
Styrene
Sulfate
tert-Butylbenzene
Tetrachloroethane
Tetrachloroethane
Tetrachloroethylene
Tetrahydrofuran
Thallium (total)
Thiobencarb (Bolero)
Toluene
Total haloacetic acids
Total polychlorinated biphenyls (PCBs)
Total trihalomethanes (TTHMs)
Toxaphene
trans-1,2-Dichloroethylene
Tribromoacetic acid
Trichloroacetic acid
Trichlorobenzene
Trichlorobenzene
Trichloroethane
Trichloroethane
Trichloroethylene
Trichlorofluoromethane
Trichloropropane
Trichlorotrifluoroethane
Trifluralin
Trimethylbenzene
Trimethylbenzene
Tritium
Uranium-234
Uranium-235
Uranium-238
Vanadium
Vinyl chloride
Information on each of these impurities can be found here.