NEW YORK, June 14 (Reuters) - U.S. municipal bond sales are expected to fall to $6.8 billion next week from this week's total of $8 billion, according to Thomson Reuters estimates released on Friday. Negotiated sales next week are expected to total $5.5 billion in 81 issues, compared with nearly $5.65 billion in 81 deals this week. The California Health Facilities Authority will sell $763.6 million of revenue bonds for the St. Joseph Health System through lead manager Morgan Stanley. A day for the sale has yet to be determined. On Monday, Moody's Investors Service revised the system's outlook to positive from stable, citing the expectation of an improved balance sheet, as well as debt and operating measures which could lead to an upgrade. The bonds are rated A1 by Moody's, AA-plus by Standard & Poor's Ratings Services and AA-minus by Fitch Ratings, with a stable outlook from S&P and Fitch. After a one-day retail order period on Monday, the New York City Municipal Water Finance Authority will sell $400 million of water and sewer system second general resolution revenue bonds through lead manager Citigroup. Among other large deals next week is a Dallas/Fort Worth International Airport $366.99 million joint revenue improvement bond issue, pricing on Thursday via lead manager Jefferies LLC. The deal is structured with serial maturities from 2026 through 2045, according to the preliminary official statement. Competitive deals are expected to total $1.3 billion in 131 sales, compared with almost $2.37 billion in 170 issues in the week ended June 14. On Tuesday, New Mexico will sell $200.1 million of bonds competitively, as well. Details were not available.