Sleeking hair for Spring/Summer 2016 season. 

Sleek hair styles are yet in for the warmest season of the year. Slightly wet hair effect will work perfectly throughout summer days by giving a perception you just came out of the sea or a swimming pool.
Messy hair don't care is kind of a motto of the season. But don't rush to cover own head with a hat, headscarf or what ever else. You can bring your slightly dirty look to a whole new, polished-much level by sleeking your hair. By the way, you don't need many styling products and appliances to achieve such a look. And just for the note, your hair doesn't necessarily need to be messy to look super sleek.
Speaking of the Spring/Summer 2016 runway examples, sleek hair look were seen at Kenzo, Dsquared2 and J. W. Anderson in quite different varieties.

Sleek and Loose

Sleek and loose hair styling is the easiest way to achieve the season look. What you will need in this styling approach is a hair gel,creme, paste or spray (a product that works on your hair the best) and a hair brush or comb. Other details may include headband, pins or any curling/straightening appliance.

Sleek and Collected

In case you want to hide your sleek hair near to completely - simply make an updo. Updo hairstyles here include low/high ponytail as well as low/high bun. What you will need here includes a styling products (gel, paste and so on) and details that will make a chosen updo work - elastic hair band and/or pins. 

Image Courtesy: Why Not Models, Vogue Runway, The Best Fashion Blog