Water has a density of 1000 kg/m3 by standard definition at its temperature of maximum density 3.98 Â°C and at 0% salinity. Scientists and engineers use water as a baseline for comparing the relative density of various materials. Water with a density of 1000 kg/m3 at 3.98 Â°C has a mass of 1000kg and a volume of 1 m3.
Spelt is a word. It is the past participle of spell. It is also a type of wheat, and therefore also a noun. It depends upon whether you are using British English (and Spelt is correct) or you are using American English.
Both spelled and spelt are old, and examples of each are easily found in historical Google Books searches covering the 17th and 18th centuries. It is true, however, that spelt was ascendant everywhere through most of the 19th century. This ended when Americans permanently settled on spelled around 1900.