We found 48 public water systems in Nassau county (ordered by population size).
| Name | Areas served | Population served | Contaminant count | Violation count |
|---|---|---|---|---|
| New York American Water - Lynbrook | Hempstead, Lynbrook | 230,300 | 218 | 0 |
| New York American Water - Merrick | Hempstead | 177,000 | 70 | 59 |
| Wa Of Western Nassau | Hempstead, North Hempstead | 120,000 | 88 | 5 |
| Town Of Hempstead Water Department | Hempstead | 110,000 | 216 | 0 |
| Jericho Wd | Oyster Bay | 58,000 | 217 | 95 |
| Hempstead (v) | Hempstead | 56,000 | 33 | 41 |
| Hicksville Wd | Oyster Bay | 47,810 | 111 | 1 |
| South Farmingdale Wd | Oyster Bay | 44,700 | 57 | 0 |
| Freeport (v) | Freeport | 43,007 | 21 | 2 |
| Manhasset Lakeville Wd | North Hempstead | 43,000 | 87 | 48 |
| Massapequa Wd | Massapequa Park, Oyster Bay | 43,000 | 50 | 84 |
| Long Beach City | Long Beach | 35,000 | 8 | 4 |
| Plainview Wd | Oyster Bay | 35,000 | 66 | 28 |
| Port Washington Wd | North Hempstead | 34,000 | 81 | 85 |
| Bethpage Wd | Oyster Bay | 33,000 | 47 | 1 |
| West Hempstead Wd | Hempstead | 32,031 | 18 | 116 |
| Jones Beach State Park | Hempstead | 30,807 | 0 | 6 |
| Glen Cove City | Glen Cove | 28,000 | 63 | 130 |
| Garden City (v) | Garden City | 25,000 | 62 | 25 |
| Rockville Centre (v) | Rockville Center | 24,700 | 40 | 88 |
| Mineola (v) | Mineola | 20,600 | 47 | 33 |
| Westbury Wd | North Hempstead, Westbury | 20,500 | 110 | 7 |
| Franklin Square Wd | Hempstead, Stewart Manor | 20,000 | 37 | 5 |
| Roslyn Wd | Roslyn | 17,000 | 64 | 55 |
| Garden City Park Wd | New Hyde Park | 15,500 | 54 | 5 |
| New York American Water - Sea Cliff | Sea Cliff | 15,000 | 25 | 3 |
| Albertson Wd | North Hempstead | 13,500 | 60 | 31 |
| Carle Place Wd | North Hempstead | 9,005 | 0 | 112 |
| Oyster Bay Wd | Oyster Bay | 8,700 | 0 | 2 |
| Farmingdale (v) | Farmingdale | 8,405 | 0 | 2 |
| Williston Park (v) | Williston Park | 7,516 | 0 | 4 |
| Locust Valley Wd | Mill Neck, Oyster Bay | 7,500 | 58 | 2 |
| Bayville (v) | Bayville | 6,700 | 0 | 29 |
| Lido-point Lookout Wd | Hempstead | 6,000 | 0 | 9 |
| Old Westbury (v) | Old Westbury | 4,700 | 0 | 2 |
| Sands Point (v) | North Hempstead, Sands Point | 2,800 | 0 | 0 |
| East Williston (v) | East Williston | 2,503 | 0 | 2 |
| Tobay Beach | Oyster Bay | 2,420 | 0 | 21 |
| Plandome (v) | Plandome | 1,600 | 0 | 8 |
| Cathedral Gardens Wd | Hempstead | 1,500 | 0 | 19 |
| Glenwood Wd | Oyster Bay | 1,000 | 0 | 1 |
| Ne Farmingdale Wd | Farmingdale | 405 | 0 | 0 |
| New York American Water - Mill Neck | Mill Neck, Oyster Bay | 240 | 0 | 4 |
| Swan Cove Water Supply | Oyster Bay | 80 | 0 | 0 |
| Seawanhaka Yacht Club | Centre Island, Oyster Bay | 60 | 0 | 0 |
| Beaver Dam Winter Sports | Matinecock, Oyster Bay | 35 | 0 | 0 |
| Centre Island Ws | Centre Island | 18 | 0 | 0 |
| Split Rock Water Supply | Centre Island, Oyster Bay | 15 | 0 | 0 |