Cementitious building components, although widely used in low-income countries, are too expensive for many applications related to low-income housing. This thesis explores three options for reducing component cost: 1. Use of local fine aggregates, often with clay contamination, instead of low-fines sands transported from a distance. 2. Improved designs, to achieve better material economy. 3. Change of production environment, from on-site to component prefabrication followed by transport to site. Water storage tanks for rainwater harvesting were used as the example for component design, and as a case-study for considering the effect of changing the production environment. The work showed that: In some cases, use of local aggregates will give a cost saving of around 10%. Improved design can give significant reduction in materials usage, of up to 40%. Off-site prefabrication of components, followed by on-site assembly to produce the desired product, does not seem preferable to the prevelant practice of entirely on-site production from raw materials. However, factory-based manufacture of complete products, followed by transport to site, has a number of attractions over entirely on-site production. Out of the three options examined, improved component design offers the greatest benefits for the case study considered.