The savings bank began its activities on 3 February 1907. It joined the group of Cajas Municipales Vasco Navarras, logically, with a similar spirit to the latter, which was different from that of the savings sections of the private banks. The City Council took responsibility for the funds, donated a small amount as initial capital, which it was not necessary to use, and ceded some municipal premises located in the old Alhóndiga, in the Plaza de los Santos Juanes. Its potential customers were in the ‘seven streets’, workers, craftsmen and vendors, as well as the men and women from the nearby hamlets who went there to sell their products; later on, neighbours from other neighbourhoods would come.
In 1912 the first branches were opened on the Rivera de Deusto and in the Plaza Circular; in 1914 in Amorebieta, Murgia, Bermeo, Amurrio, Miravalles, Llodio, Durango, Gernika, Lekeitio, Markina, Elorrio, Mundaka; in 1921 in Portugalete, Barakaldo, Plentzia, Sopuerta, Gallarta, plus other urban branches in the capital and in Burgos (Espinosa de los Monteros, Medina de Pomar and Villarcayo, the latter offices having to be ceded after the civil war, under pressure from the Caja de Ahorros Municipal de Burgos to which it passed control, since the legislation at the time limited the activity of the savings banks to their original province). In 1927, 42 branches were open.
Until 1914 it grew slowly, but from that date onwards its balances increased notably, due to the suspension of payments of the Crédito de la Unión Minera, which led savings to seek shelter in a better-backed institution considered more secure for family savings. From that moment on, its development was spectacular. As can be seen in the following table. Twenty years after its opening, in 1927, it was the third largest savings bank among the federated savings banks and the largest in the Confederación de Cajas Vasco Navarras (Confederation of Basque-Navarre Savings Banks). Savings balances continued to rise throughout this period and there was only a slight dip in 1939, which is understandable if one takes into account the circumstances Bizkaia was going through in the year of the end of the Civil War.
| Urtea | Ezarleak | Saldoak Pezetatan. |
| 1907 1910 1920 1930 1935 1936 1939 1940 | 1.181 4.052 52.360 137.109 149.552 155.162 179.026 184.627 | 995.213 2.985.539 75.336.487 188.417.532 186.215.794 188.128.125 187.006.632 190.575.982 |
There is something very peculiar about the statutes of this savings bank, which were amended on 3 November 1924. While it was normal in these institutions to speak of the leading role that the savings of the humblest were to play, the statutes of the Municipal de Bilbao stated that it was destined to ‘receive the savings entrusted to it by all social classes, to use them in operations that would give them complete security’, They did not close their doors to anyone and employed an economic pragmatism that was very noteworthy and not surprising considering the powerful competitors they had in the Biscayan banks which, despite specialising in large industry, mining and commerce, were not averse to attracting popular savings either.
The Caja de Ahorros began its operations with ordinary passbooks, which would later be extended to school savings books (1915), fixed-term deposits, current accounts, corporate accounts, etc... Investments, which were initially made at the discretion of the director and the Council, subsequently had to be adapted to the regulations dictated by the State. The City Council had a borrowing account which it used to attend to public works or other needs (in 1930 it was 6,423,112 pesetas); it provided loans secured by mortgages, securities, personnel, and on jewellery, clothes and other garments (Monte de Piedad); credit accounts and special credits. It also provided the province with other services free of charge, such as payment of salaries to the clergy and teachers in Bizkaia.
Among the mortgage loans it made, those for the purchase of farmhouses under very special conditions should be highlighted. The loan covered 75% of the value of the farmhouse at an interest rate of 4.5% (1927) and for a period of twenty years. The maximum amount lent was 20,000 pesetas. It also granted up to a maximum of 10,000 pesetas for the extension, renovation and sanitation of the farmhouses inhabited by their owners.
The same applies to those dedicated to alleviating the serious housing problem. To facilitate the implementation of the Ley de Casas Baratas (1922), the C.A.M. provided significant financial aid, advancing up to 70% of the value of the budget to the cooperatives for the construction of cheap houses, until the money from the State arrived. When the state subsidies ended, the C.A.M. continued to provide long-term, low-interest loans. In 1921 it built a block of houses for rent to middle-class families in the Ensanche (the maximum rent was 125 pesetas). A total of 213 spacious homes with lifts, bathrooms and heating. But this operation did not have the social purpose of cheap houses; it was a way of diversifying investments, doing so in a property from which a similar income could be obtained to other investment operations of the Caja, although with less risk.
