iphone 5c water damage - can hear alerts come through when turned on - screen starts black slowly fades to white with lines all over - what to do next?

Take it to Apple for a free hardware evaluation. Odds are that there is internal damage from short circuits caused by the water and you will have to replace it. You cannot repair damaged solid state circuits once they've been shorted out.

I second Micael's solution

Like Mark_pro said on an other topic

You have a few options here.

1. If your only concern is to have a working phone and cost is not a factor, then your best option would be to have Apple replace the device under their out of warranty replacement program.

2. If, however, your data is important then you'll need to pursue a 3rd party who specializes in liquid damage data recovery.

3. Take it to a local 3rd party repair shop to have it diagnosed. Often liquid damaged devices can be easily repaired by replacing a few parts or a simple cleaning. It is important to find a place that will remove the EMI shields on the logic board and properly clean the entire board though. Often these places will not charge for the time it takes to look at and diagnose the phone and if repair is possible it will be much cheaper than replacing the entire phone

Repairing a liquid damaged device for the sake of the device is always a gamble though, and I'd recommend the first option for long term reliability, the second option if your data is the most important factor, and the 3rd option if you can't afford the first.

You might want to mention that if someone opts to take it to a 3rd party for diagnosis or repair, they will permanently forfeit all rights to service from Apple if the device is physically opened.