Water hardness is caused almost entirely by calcium and magnesium ions. Other di- and trizalent metals have a similar effect, but usually are not present in high enough concentration in potable waters to cause problems. Hardness increases soap consumption in laundries and causes scale in boilers. Hardness test kits include the inexpensive Models 5-B and 5-EP designed for those needing quick checks on the efficiency of water softeners. More sophisticated test kits allow the determination of total hardness as well as calcium and magnesium (by difference).