How many times should I press this?
JavaScript (ES6) 77 66 64 60 bytes
(Saved some bytes thanks to @Johan Karlsson and @Arnauld).
s=&gt;[...s].map(l=&gt;s=~~s+2+'behknquxcfilorvysz'.search(l)/8)|s



f=

s=&gt;[...s].map(l=&gt;s=~~s+2+'behknquxcfilorvysz'.search(l)/8)|s

console.log(f(''));                 //0
console.log(f('water'));            //8
console.log(f('soap'));             //9
console.log(f('candela'));          //13
console.log(f('code golf'));        //20
console.log(f('king of the hill')); //33