Water is an invaluable resource that is required for all life forms, and it is necessary for civilization. However, water is a globally scarce resource, and it is estimated that humanity will at some point struggle to attain adequate water to sustain their needs [
1,
2,
3]. Therefore, it is necessary to assess and detail the water footprints in all sectors of the economy. Water footprint assessment has in recent years been recognized as a significant sustainability indicator within the agricultural and biofuels sector [
4,
5]. The water footprint concept takes cognisance of the total volume of freshwater consumed in the production of a product, and it is measured throughout the entire value chain right from the stage of producing the inputs until the final product reaches the consumer [
6,
7,
8]. Aldaya, Chapagain, Hoekstra, and Mekonnen [
8] categorize water footprint measured along the entire value chain into blue, green, and grey. The blue water footprint is the surface and groundwater consumed along the value chain, including the water that was evaporated and water that was incorporated into the product. The green water footprint refers to all the rainwater that is consumed by the crop, excluding water that becomes run-off. The grey component of water footprints is the volume of freshwater required to assimilate pollutants to accepted quality standards. The water footprint concept is elaborated in the Water footprint Assessment Manual described by Aldaya, Chapagain, Hoekstra, and Mekonnen [
8]. Water footprint assessment has gained prominent attention in the agricultural and biofuel sectors (more significantly first-generation biofuels) because the majority of the global water resources are used within the agricultural sector; therefore, sustaining current agricultural conditions and exploring further activities such as biofuel production within the agricultural sector requires adequate approaches for the sustainable use of the limited water resources [
5,
9]. Biodiesel is a form of biofuel produced from oil crops such as sunflower, amongst others, and its production process and the respective amounts of water used in the biodiesel production process have been evaluated worldwide. For instance, various assessments have been conducted in Italy, Greece Argentina, the USA, and South Africa looking into the viability of sunflower as a biodiesel feedstock with several comparisons to other oil crops such as algae, canola, and soy beans [
9,
10,
11]. Water footprint assessments have been conducted in various parts of the world such as Tuscany, Spain, South Africa, etc., to estimate the volumes of water that are used to grow sunflower as a feedstock and volumes of water used throughout the entire sunflower-biodiesel production process [
2,
5,
10,
12]. Furthermore, the sustainability of feedstock production has been observed worldwide [
5,
8]. There is a plethora of information related to biodiesel production from various feedstock crops worldwide. However, in South Africa, this body of information is typically focused on the water requirements of the crops, usually fixated on crop irrigation and the volumes of water required to optimize yield, without much consideration of consumptive water use throughout the entire production process and green water stress. Even though Mekonnen and Hoekstra [
13] estimated the water footprint of biodiesel produced in South Africa, this was mainly based on global average data, whilst the water footprint assessments of biodiesel production performed by Pahlow, Snowball, and Fraser [
5] for South Africa, were based upon data ranging from 1996 to 2005 derived from Mekonnen and Hoekstra [
13]. There have not been any recent assessments of the water footprint of biodiesel in the country. Therefore, little information is available to help inform and guide policymakers in formulating policies for sustainable water use and management in the process of producing biodiesel from feedstock crops in the current era. South Africa is a water-scarce country, ranked as the 30th driest country in the world. It has 22 water source areas that are primarily fed by rainfall. However, about 60% of the national river ecosystems are threatened, whilst approximately 23% are critically endangered and only about 16% of the water sources are protected as nature reserves or parks [
14]. It is therefore important to monitor, restore, maintain, and manage water resources to secure and sustain the available water supplies and to protect these water sources. Furthermore, the majority of these scarce water resources are used within the agricultural sector, which consumes about 60%, whilst contributing about 2% to the national GDP [
15]. In addition, embarking on further agricultural activities to incorporate biodiesel production requires an agricultural feedstock crop that does not impose any further adverse effects on water resources.
Due to its low water use characteristics and high tolerance to drought conditions, the sunflower crop has been endorsed as a biodiesel feedstock crop in South Africa [
16,
17]. Furthermore, sunflower is largely available nationally, and it constitutes about 70% of the national oilseeds [
18]. Additionally, fossil fuel prices are rapidly increasing, and for South Africa, this poses a socio-economic threat for the population at large, and this instigates for the nation to delve into the production and use of alternative fuels such as biodiesel. Thus considering that sunflower can be produced across almost all provinces of South Africa and at adequate volumes, it is therefore important to provide ample attention on the production of sunflower as a biodiesel feedstock, more significantly in line with its water use throughout the entire biodiesel value chain. So as to attain a better understanding of the potential effects and the impact of sustainable productivity on water resources and potential paths for the efficient use of water resources in the production of biodiesel from sunflower. Therefore, this current paper embarks on assessing the water footprint of producing biodiesel from sunflower grown under rain-fed and irrigated production systems in South Africa. The irrigation system provides supplementary irrigation to meet the rainfall shortfall of the crop water requirement. In addition, the impact of sunflower feedstock on local water stress and sustainability at the local river basin was also assessed.