The decrease of organic matter content in agricultural soils is a problem of great concern to farmers around the world. Indeed, it lowers soil fertility that directly impairs agricultural crop production and affects a number of other soil properties like water retention capacity, aggregation and structure formation, soil mechanical strength or compactibility. Scarcity in plant available water poses a risk to agriculture, especially in drought-prone areas. However, the increase of organic waste recycling in agriculture may also lead to an increase in soil organic matter contents and to changes in related soil properties. Here, we review 17 long-term field experiments (≥9 years) that investigated the effects of organic amendments on organic carbon and water availability in topsoils. We paid particular attention to the effects of added organic matter on soil bulk density or porosity and consequently on plant available water. Our main findings are that (1) plant available water generally improves after organic waste addition (relative changes from −10 to +30 vol%; p = 0.052), (2) organic matter quality affects changes in organic carbon (p < 0.05), (3) it is more suitable for plant available water quantification to use volumetric rather than gravimetric water con-