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.
This is a lot more expensive than the Water Corp's estimate of seawater desalination cost in 1987 of $ 1.45 per kilolitre (WAWA, Planning Future Sources For Perth's Water Supply, ISBN 0 7244 6743 2).he latest Report on desalination for the QLD gov't puts the cost at $ 2.55 per kilolitre for a similar sized plant to the WA one at Kwinana. The seawater desalination plant at Kwinana has a capital cost according to the Water Corporation of $387 million.