These hardness test strips are not only perfect for testing the total hardness in your tap water but also the effectiveness of filters such as Brita. Brita and other filters don't just remove odor and taste from your tap water. They also remove calcium and magnesium - the number-one destroyer of espresso machines. So even if you use a filter, testing the water coming out of your filter is still a good idea because it gives you a clearer idea of how often to replace the filter. Each package contains two test strips. Protect your investment: test your water often.