Based on MMAT, nine studies scored 100% [17,18,19,20,21,22, 24, 29, 32]. Of these, two were qualitative, five were quantitative descriptive, and one was a mixed-methods study. Nine studies scored 75% [16, 23, 25,26,27,28, 31, 33, 34] among these, three were experimental studies that had no information on blinding [23, 33, 34]; three were qualitative studies with no clear description regarding the influence of the researcher on study findings [25, 27, 31]; two were mixed methods studies that did not highlight the limitations to integration of qualitative and quantitative findings [16, 28]; and one was a non-randomised study with a low response rate . Two qualitative studies scored 50% each because they lacked information about how data were analysed and description on whether a special consideration was given to how findings related to the researcher’s influence [7, 30]. MMAT has no cut-off point for the quality of studies, but we considered ‘less than 50%’ score as low quality. However, none of our selected studies scored below 50%. With an average MMAT score of 82.5% across the included studies, the studies are considered to be of high quality.
Twenty studies met the eligible criteria. Of these, six were conducted in Uganda [7, 26, 28, 32,33,34], two in Ethiopia [17, 23], and two in Tanzania [20, 29]. Furthermore, one study was conducted in each of the following countries: Zambia , Zimbabwe , Kenya , Nigeria , Haiti , Malawi , Ghana  and Sierra Leone ( (See Table 2). In terms of study design, six qualitative studies [7, 18, 25, 27, 30, 32], 11 quantitative studies [17, 19, 20, 22,23,24, 26, 29, 31, 32, 34], and three mixed methods studies [16, 21, 28] were evaluated. Data collection in the qualitative studies was through focus group interviews, semi-structured questionnaire and in-depth interviews. The quantitative studies utilised quasi-experiment, pre-post survey, cross-sectional survey and cluster randomised trials study approaches (see Table 2).
A total of 11 studies were conducted in the community [7, 16, 17, 19,20,21,22,23, 25,26,27,28,29,30] and four were conducted in schools [18, 24, 28, 34]. The study population in six studies were children while 16 studies were conducted with adults. The youngest participants were infants less than 8 months old  and the oldest was 40 years  The number of participants in each study varied from 21  to 2875 .
Summary of the findings
Studies included in this review were analysed based on the following three outcomes: the use and benefit of tippy-tap in promoting hand hygiene; adoption of tippy-tap and its associated hand hygiene resources, and the effectiveness of tippy-tap. These sub-categories were generated from the objective of the study. The presentation and interpretation of the results follow these categories as narrated below.
Use and benefits of tippy-tap in promoting hand hygiene
The use of tippy-taps for handwashing among household members or school children was reported by authors of 16 studies conducted in Nigeria, Haiti, Malawi, Ghana, India, Tanzania, Uganda, Sierra Leone, Kenya and Ethiopia [7, 16, 17, 19,20,21,22,23,24,25,26, 28,29,30,31, 34]. The use of tippy-tap among the participants in the 16 studies ranged from 2.7%  to 80% .
Concerning the benefits of using tippy-taps, authors of three studies [7, 23, 34] reported an increase in handwashing practice by participants after being exposed to tippy-tap. In a randomised controlled trial in Uganda four intervention and four control schools were recruited into the study . At each school, one classroom was selected randomly (lottery draw), and 25 boys and 25 girls (Grades 2–5) were selected from that classroom using a systematic random sampling design (every third girl and boy). Data were collected at three waves of 1 month apart intervals. The first wave was a baseline survey that was followed by the provision of soap and handwashing education to four intervention schools. The second wave was followed by the introduction of tippy-taps and provision of soap to the intervention group. Lastly, the post-intervention survey was carried out at the last wave. The four control schools received health education only through-out the experiment and were provided with tippy-taps post-study interventions. The researchers reported an increased estimate in the proportion of students reporting ‘always’ or ‘often’ washing their hands at school from 3.5% at baseline to 100.0% at follow-up (t = 19.54, P < 0.05, 95% CI 1.21–1.68) in the intervention schools. When the similar intervention was replicated in the control schools by Time 3, there was an increase in handwashing (t = 12.92, P < 0.05, 95% CI 1.48–2.45] . In the same study, it was observed that the proportion of students ‘always’ washing their hands after using the toilet increased from 5.5 to 65.0% (t = 14.61, P < 0.05, 95% CI 1.02–1.58) in the intervention schools, while in the control schools it only increased from 3.6 to 79.3% (t = 13.21, P < 0.05, 95% CI 1.16–1.90) by Time 3 when the same intervention was replicated .
In addition, compared to control schools, introduction of tippy-taps increased the use of soap by students in the intervention schools in an experiential study from 13.5 to 84.5% (t = 5.64, P < 0.05, 95% CI 0.29–1.04); handwashing from 5.5 to 93.0% (t = 9.84, P < 0.05, 95% CI 0.98–1.91) and handwashing after using the toilet from 5.5 to 65.0% (t = 14.61, P < 0.05, 95% CI 1.02–1.58) . Similarly, another study  found that tippy-taps increased handwashing after latrine use by providing convenient soap and water, and by acting as a salient cue to handwashing. Although quantitative data on handwashing rates were not collected, participants in households with tippy-taps believed that their post-latrine handwashing rates had increased as a result of the tippy-taps . Pre- and post-data analysis on self-reported handwashing revealed that the population-tailored interventions, especially the tippy-tap-promotion, performed better than the standard education intervention (education intervention, the f-diagram exercise, an often applied intervention tool) . In a study conducted by Christensen and colleagues , the use of tippy-tap was measured through the availability of handwashing resources (soap and water) at the tippy-tap station. These researchers found that enumerator-observed indicators of use were still high (72–85% for having both soap and water present at the tippy-tap station) . In an Indian qualitative study, most participants reported using tippy-tap because of its benefits . The participants reported that handwashing using tippy-tap requires less water and soap compared to the usual method of handwashing . However, in the same study  participants indicated the following as challenges of the tippy-tap handwashing technology: it was not easy to wash hands of very young children with the tippy-tap; there was a potential problem that older children may play with the device, thus destroying it or wasting water; it was also recognized that the device required extra water, time, and work to install, use, and maintain. In addition, a study by Biran , one participant suggested that tippy-taps did not look attractive, elderly participants said tippy-taps looked childish and unnecessary, and that people used to live longer even before tippy-taps were developed.
On the other hand, the economic benefits of tippy-taps were reported by the authors of a Nigerian study . The installation of tippy-taps in small scale business facilities by women who were involved in selling food items led to an increase in the number of customers, which resulted in more sales and profits.
Adoption of tippy-tap and its associated hand hygiene resources
Authors of six studies assessed the adoption of tippy-taps by households [7, 18, 22, 23, 32, 33]. In a study conducted by Christensen , the intervention households were significantly more likely to have a place for handwashing (71–85 percentage point increases) with soap available (49–66 percentage point increases) than controls. These authors also noted an increase of 86% in having a dedicated location for tippy-taps. Similarly, in another study, teachers educated school going children on tippy-tap as a handwashing station . Although these children were not directly asked to construct tippy-tap, they all managed to attempt building one or influence their parents to assist them. Their parents trusted the information received from their children. The tippy-taps were also found to be attractive, easy to use and helpful in fostering the habit of handwashing among children .
Signh et al.  engaged the community in a hand hygiene promotion program. At 1 year follow-up, the researchers noted a 47% installation of functioning tippy-taps in the intervention villages compared to 35% in the control villages (p < 0.002) . There was a significant increase in tippy-tap installation by community members from 4.7% of households at baseline to 47% of homes after the intervention, following the demonstrations to construct the device by community health volunteers (CHVs). The CHVs were trained on the tippy tap construction and acted as role models to other community members. Furthermore, there was a great improvement in owning tippy-taps by CHVs from 1% at baseline to 84% after interventions . Another significant evidence of adoption of tippy-taps was observed in a study where all study households built tippy-taps within 2 weeks of counselling . After 1 year of tippy-tap promotion, 80% of the households still had a tippy-tap installed, with evidence of use (water in the container and on the ground around the device). Similar results were observed in a study by Contzen and colleagues  in which, close to 100% of the households followed the promotion and invested material and time to construct their tippy-tap. In the same study, all participants in the intervention group constructed tippy-taps and about 83% of these were still operational 3 months after termination of the interventions.
Although there is limited awareness on tippy-tap, having knowledge about tippy-tap did not result in immediate construction of the station [7, 18]. The researcher thought that study participants constructed a tippy-taps because they were asked to do so, or they anticipated that the researcher would be visiting them regularly to evaluate the adoption of the technology . Some participants constructed tippy-tap as a result of campaigns and fear of fines from community leaders .
Effectiveness of tippy-tap
Out of twenty articles under review, only one study  had an incidence of diarrhoea as an outcome measure. The study was conducted in a school setting in Uganda and aimed at measuring the efficacy of a tippy-tap-based handwashing programme in promoting handwashing rates in elementary schools in rural Uganda. Zhang and colleagues  used the pre-and post-intervention surveys in which four intervention schools were given tippy-taps, soap and educational materials, while four control schools initially received only educational materials. Proxy data for assessing the effectiveness of tippy-taps in reducing diarrhoeal disease was indicated by the number of students reporting stomach pain episodes in the previous month. The authors of the study found that in the intervention schools, the percentage of students reporting no stomach pain episodes increased from 7% at baseline to 80% after the intervention (t = 10.84, P < 0.05, 95% CI 0.92–1.68) . However, no proxy data was provided on the trend of diarrhoea in the control group.