In rural areas of developing countries, participation of all stakeholders in water supply projects is an important step towards further development. As most of the beneficiaries are usually women, it is especially important to involve them in order to achieve sustainable and successful water supply projects. Women are responsible for management of the water inside and outside their home, and they often spend more than 6 hours daily to fetch drinking water from distant water sources. The problem is that rural women have a weak role in the water supply projects’ phases in rural Yemen. Therefore, this research focuses on analyzing the causes of the lack of women's participation in rural water supply projects, and in what ways women's participation could contribute to sustainable water supply projects in rural mountainous areas in Yemen. Four water supply projects were selected as a case study in Al-Della'a Alaala sub-district in Al-Mahweet governorate. Two of them were implemented by Social Fund and Development (SFD), and the others were implemented by General Authority for Rural Water Supply Projects (GARWSSP). Furthermore, Al-Galba project, which succeeded by involvement of rural women and is located in Badan district in Ibb governorate, was selected for comparison. For this purpose, I carried out a literature review of academic journals, books from Internet websites, international documents, and reports of the GARWSSP and SFD which are related to the four water supply projects, in order to identify the general principles for impact identification and significance determination. The other source for data collection was the opinion of eight Yemeni water experts working in the water sector and academic institutions, in order to investigate their point of view as a specialized group about the reasons for and challenges of the lack of women’s participation. Then face-to-face interviews were carried out with 50 different stakeholders (from a governmental agency, a donor's agency and the local community) in the five water supply projects to find out about their opinion on the criteria for sustainable rural water supply projects and the consequences if rural women are not involved in water supply projects, as well as the barriers for their participation. The potential consequences of active rural women's participation in the water projects are improved continuity, improved maintenance, protected equipment’s, and improvement of the health and education situations in these areas. The majority of the respondents from GARWSSP’ projects estimated that there is no reason to involve women in the project activities. In the comparison project - in which a woman worked as a supervisor and implemented the project – on the other hand, 100% of responders indicated that women’s participation is vital for sustainability. Therefore, the results of this research will hopefully contribute to an improvement of the conditions that are needed to stimulate rural women's participation in the mountainous areas of Yemen.