| MRWA | Main Roads Western Australia 
| Others |
| MRWA | Maine Rural Water Association
| Others |
| MRWA | Maryland Rural Water Association
| Others |
| MRWA | Melbourne Retail Water Agencies
| Others |
| MRWA | Merseyside Recycling and Waste Authority
| Others |
| MRWA | Merseyside Recycling and Waste Authority formerly known as Merseyside Waste Disposal Authority
| Others |
| MRWA | Michigan Rural Water Association
| Others |
| MRWA | Midland Railway of Western Australia
| Others |
| MRWA | Minnesota River Watershed Alliance
| Others |
| MRWA | Minnesota Rural Water Association
| Others |
| MRWA | Missouri Rural Water Association
| Others |
| MRWA | Montour Run Watershed Association
| Others |
| MRWA | Muskegon River Watershed Assembly
| Others |