The safe disposal of human excreta is of paramount importance for the health and welfare of populations living in low income countries as well as the prevention of pollution to the surrounding environment. On site sanitation (OSS) systems are the most numerous means of treating excreta in low income countries, these facilities aim at treating human waste at source and can provide a hygienic and affordable method of waste disposal. However, current OSS systems need improvement and require further research and development. Development of OSS facilities that treat excreta at, or close to, its source require knowledge of the waste stream entering the system. Data regarding the generation rate and the chemical and physical composition of fresh faeces and urine was collected from the medical literature as well as the treatability sector. The data were summarised and statistical analysis was used to quantify the major factors that were a significant cause of variability. The impact of this data on biological processes, thermal processes, physical separators and chemical processes was then assessed. Results showed that the median faecal wet mass production was 128 g/cap/day, with a median dry mass of 29 g/cap/day. Faecal output in healthy individuals was 1.20 defecations per 24 hour period and the main factor affecting faecal mass was the fibre intake of the population. Faecal wet mass values were increased by a factor of 2 in low income countries (high fibre intakes) in comparison to values found in high income countries (low fibre intakes). Faeces had a median pH of 6.64 and were composed of 74.6% water. Bacterial biomass is the major component (25-54% of dry solids) of the organic fraction of the faeces. Undigested carbohydrate, fibre, protein and fat comprise the remainder and the amounts depend on diet and diarrhoea prevalence in the population. The inorganic component of the faeces is primarily undigested dietary elements that also depend on dietary supply. Median urine generation rates were 1.42 litres/cap/day with a dry solids content of 59 g/cap/day. Variation in the volume and composition of urine is caused by differences in physical exertion, environmental conditions as well as water, salt and high protein intakes. Urine has a pH 6.2 and contains the largest fractions of nitrogen, phosphorus and potassium released from the body. The urinary excretion of nitrogen was significant (10.98 g/cap/day) with urea the most predominant constituent making up over 50% of total organic solids. The dietary intake of food and fluid is the major cause of variation in both the faecal and urine composition and these variables should always be considered if the generation rate, physical and chemical composition of faeces and urine is to be accurately predicted.