Tags are very common in spoken English, and have many functions. One of the common functions is to start a conversation or help keep it going. The two basic rules about tag questions are:1  If the statement is negative, the tag must be positive.ags are very common in spoken English, and have many functions. One of the common functions is to start a conversation or help keep it going. The two basic rules about tag questions are:
The average cost for a community to fluoridate its water is estimated to range from approximately $0.50 a year per person in large communities to approximately $3.00 a year per person in small communities. For most cities, every $1 invested in water fluoridation saves $38 in dental treatment costs.55 âFor most cities, every $1 invested in water fluoridation saves $38 in dental treatment costs.â It can be calculated from these data that the average lifetime cost per person to fluoridate a water system is less than the cost of one dental filling.
Costs vary, but the lowest price for desalinated seawater from a reverse osmosis plant is around $750 an acre-In the U.S., water-strapped California leads in both water innovations and needs. foot (325, 851 gallons) â more than double the average cost of groundwater.owever, desalination is expensive, energy-intensive, and can damage marine ecosystems. Moreover, while seawater accounts for 60 percent of desalinated water today, Sedlak and others say itâs much more practical and sustainable to desalinate less-salty brackish water and use the technology to recycle wastewater.